diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 7b06c6ab5..7459b628d 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -4,4 +4,5 @@
 
 ## Other code changes
 
-* no changes
\ No newline at end of file
+* no changes
+
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv40_50/resources40_50/ActivityDefinition40_50.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv40_50/resources40_50/ActivityDefinition40_50.java
index 7d046c543..0ecc71ced 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv40_50/resources40_50/ActivityDefinition40_50.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv40_50/resources40_50/ActivityDefinition40_50.java
@@ -1,5 +1,6 @@
 package org.hl7.fhir.convertors.conv40_50.resources40_50;
 
+import org.hl7.fhir.convertors.VersionConvertorConstants;
 import org.hl7.fhir.convertors.context.ConversionContext40_50;
 import org.hl7.fhir.convertors.conv40_50.datatypes40_50.general40_50.CodeableConcept40_50;
 import org.hl7.fhir.convertors.conv40_50.datatypes40_50.general40_50.Identifier40_50;
@@ -19,6 +20,7 @@ import org.hl7.fhir.convertors.conv40_50.datatypes40_50.primitive40_50.Uri40_50;
 import org.hl7.fhir.convertors.conv40_50.datatypes40_50.special40_50.Dosage40_50;
 import org.hl7.fhir.convertors.conv40_50.datatypes40_50.special40_50.Reference40_50;
 import org.hl7.fhir.exceptions.FHIRException;
+import org.hl7.fhir.r5.model.CodeType;
 import org.hl7.fhir.r5.model.CodeableReference;
 
 /*
@@ -295,9 +297,10 @@ public class ActivityDefinition40_50 {
       case SUPPLYREQUEST:
         tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.SUPPLYREQUEST);
         break;
-//      case TASK:
-//        tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.TASK);
-//        break;
+      case TASK:
+        tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.NULL);
+        tgt.addExtension(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME, new CodeType("Task"));
+        break;
       case VISIONPRESCRIPTION:
         tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.VISIONPRESCRIPTION);
         break;
@@ -312,8 +315,11 @@ public class ActivityDefinition40_50 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.r4.model.Enumeration<org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind> tgt = new org.hl7.fhir.r4.model.Enumeration<>(new org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKindEnumFactory());
-    ConversionContext40_50.INSTANCE.getVersionConvertor_40_50().copyElement(src, tgt);
-    switch (src.getValue()) {
+    ConversionContext40_50.INSTANCE.getVersionConvertor_40_50().copyElement(src, tgt, VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME);
+    if (src.hasExtension(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME)) {
+      tgt.setValueAsString(src.getExtensionString(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME));
+    } else {
+      switch (src.getValue()) {
       case APPOINTMENT:
         tgt.setValue(org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind.APPOINTMENT);
         break;
@@ -353,15 +359,13 @@ public class ActivityDefinition40_50 {
       case SUPPLYREQUEST:
         tgt.setValue(org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind.SUPPLYREQUEST);
         break;
-//      case TASK:
-//        tgt.setValue(org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind.TASK);
-//        break;
       case VISIONPRESCRIPTION:
         tgt.setValue(org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind.VISIONPRESCRIPTION);
         break;
       default:
         tgt.setValue(org.hl7.fhir.r4.model.ActivityDefinition.ActivityDefinitionKind.NULL);
         break;
+      }
     }
     return tgt;
   }
diff --git a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv43_50/resources43_50/ActivityDefinition43_50.java b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv43_50/resources43_50/ActivityDefinition43_50.java
index bcf5e6d98..3a9b39bba 100644
--- a/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv43_50/resources43_50/ActivityDefinition43_50.java
+++ b/org.hl7.fhir.convertors/src/main/java/org/hl7/fhir/convertors/conv43_50/resources43_50/ActivityDefinition43_50.java
@@ -1,5 +1,6 @@
 package org.hl7.fhir.convertors.conv43_50.resources43_50;
 
+import org.hl7.fhir.convertors.VersionConvertorConstants;
 import org.hl7.fhir.convertors.context.ConversionContext43_50;
 import org.hl7.fhir.convertors.conv43_50.datatypes43_50.general43_50.CodeableConcept43_50;
 import org.hl7.fhir.convertors.conv43_50.datatypes43_50.general43_50.Identifier43_50;
@@ -19,6 +20,7 @@ import org.hl7.fhir.convertors.conv43_50.datatypes43_50.primitive43_50.Uri43_50;
 import org.hl7.fhir.convertors.conv43_50.datatypes43_50.special43_50.Dosage43_50;
 import org.hl7.fhir.convertors.conv43_50.datatypes43_50.special43_50.Reference43_50;
 import org.hl7.fhir.exceptions.FHIRException;
+import org.hl7.fhir.r5.model.CodeType;
 import org.hl7.fhir.r5.model.CodeableReference;
 
 /*
@@ -295,9 +297,10 @@ public class ActivityDefinition43_50 {
       case SUPPLYREQUEST:
         tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.SUPPLYREQUEST);
         break;
-//      case TASK:
-//        tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.);
-//        break;
+      case TASK:
+        tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.NULL);
+        tgt.addExtension(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME, new CodeType("Task"));
+        break;
       case VISIONPRESCRIPTION:
         tgt.setValue(org.hl7.fhir.r5.model.ActivityDefinition.RequestResourceTypes.VISIONPRESCRIPTION);
         break;
@@ -312,8 +315,11 @@ public class ActivityDefinition43_50 {
     if (src == null || src.isEmpty())
       return null;
     org.hl7.fhir.r4b.model.Enumeration<org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType> tgt = new org.hl7.fhir.r4b.model.Enumeration<>(new org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceTypeEnumFactory());
-    ConversionContext43_50.INSTANCE.getVersionConvertor_43_50().copyElement(src, tgt);
-    switch (src.getValue()) {
+    ConversionContext43_50.INSTANCE.getVersionConvertor_43_50().copyElement(src, tgt, VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME);
+    if (src.hasExtension(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME)) {
+      tgt.setValueAsString(src.getExtensionString(VersionConvertorConstants.EXT_ACTUAL_RESOURCE_NAME));
+    } else {
+      switch (src.getValue()) {
       case APPOINTMENT:
         tgt.setValue(org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType.APPOINTMENT);
         break;
@@ -353,15 +359,13 @@ public class ActivityDefinition43_50 {
       case SUPPLYREQUEST:
         tgt.setValue(org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType.SUPPLYREQUEST);
         break;
-//      case TASK:
-//        tgt.setValue(org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType.TASK);
-//        break;
       case VISIONPRESCRIPTION:
         tgt.setValue(org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType.VISIONPRESCRIPTION);
         break;
       default:
         tgt.setValue(org.hl7.fhir.r4b.model.ActivityDefinition.RequestResourceType.NULL);
         break;
+      }
     }
     return tgt;
   }
diff --git a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/Base.java b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/Base.java
index 13f3c447a..fcdfc547a 100644
--- a/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/Base.java
+++ b/org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/Base.java
@@ -319,6 +319,9 @@ private Map<String, Object> userData;
 	// -- converters for property setters
 	
   public Type castToType(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Type)
       return (Type) b;
     else if (b.isMetadataBased())
@@ -329,6 +332,9 @@ private Map<String, Object> userData;
   
 
 	public BooleanType castToBoolean(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof BooleanType)
 			return (BooleanType) b;
 		else
@@ -336,6 +342,9 @@ private Map<String, Object> userData;
 	}
 	
 	public IntegerType castToInteger(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof IntegerType)
 			return (IntegerType) b;
 		else
@@ -343,6 +352,9 @@ private Map<String, Object> userData;
 	}
 	
 	public DecimalType castToDecimal(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof DecimalType)
 			return (DecimalType) b;
     else if (b.hasPrimitiveValue())
@@ -352,6 +364,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Base64BinaryType castToBase64Binary(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Base64BinaryType)
 			return (Base64BinaryType) b;
 		else
@@ -359,6 +374,9 @@ private Map<String, Object> userData;
 	}
 	
 	public InstantType castToInstant(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof InstantType)
 			return (InstantType) b;
 		else
@@ -366,6 +384,9 @@ private Map<String, Object> userData;
 	}
 	
 	public StringType castToString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof StringType)
 			return (StringType) b;
 		else if (b.hasPrimitiveValue())
@@ -375,6 +396,9 @@ private Map<String, Object> userData;
 	}
 	
   public UriType castToUri(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof UriType)
       return (UriType) b;
     else if (b.hasPrimitiveValue())
@@ -384,6 +408,9 @@ private Map<String, Object> userData;
   }
   
   public UrlType castToUrl(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof UrlType)
       return (UrlType) b;
     else if (b.hasPrimitiveValue())
@@ -393,6 +420,9 @@ private Map<String, Object> userData;
   }
   
   public CanonicalType castToCanonical(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof CanonicalType)
       return (CanonicalType) b;
     else if (b.hasPrimitiveValue())
@@ -402,6 +432,9 @@ private Map<String, Object> userData;
   }
   
 	public DateType castToDate(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof DateType)
 			return (DateType) b;
 		else if (b.hasPrimitiveValue())
@@ -411,6 +444,9 @@ private Map<String, Object> userData;
 	}
 	
 	public DateTimeType castToDateTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof DateTimeType)
 			return (DateTimeType) b;
 		else if (b.fhirType().equals("dateTime"))
@@ -420,6 +456,9 @@ private Map<String, Object> userData;
 	}
 	
 	public TimeType castToTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof TimeType)
 			return (TimeType) b;
 		else
@@ -427,6 +466,9 @@ private Map<String, Object> userData;
 	}
 	
 	public CodeType castToCode(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof CodeType)
 			return (CodeType) b;
 		else if (b.isPrimitive())
@@ -436,6 +478,9 @@ private Map<String, Object> userData;
 	}
 	
 	public OidType castToOid(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof OidType)
 			return (OidType) b;
 		else
@@ -443,6 +488,9 @@ private Map<String, Object> userData;
 	}
 	
 	public IdType castToId(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof IdType)
 			return (IdType) b;
 		else
@@ -450,6 +498,9 @@ private Map<String, Object> userData;
 	}
 	
 	public UnsignedIntType castToUnsignedInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof UnsignedIntType)
 			return (UnsignedIntType) b;
 		else
@@ -457,6 +508,9 @@ private Map<String, Object> userData;
 	}
 	
 	public PositiveIntType castToPositiveInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof PositiveIntType)
 			return (PositiveIntType) b;
 		else
@@ -464,6 +518,9 @@ private Map<String, Object> userData;
 	}
 	
   public MarkdownType castToMarkdown(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof MarkdownType)
 			return (MarkdownType) b;
     else if (b.hasPrimitiveValue())
@@ -473,6 +530,9 @@ private Map<String, Object> userData;
 	}
 		
   public Annotation castToAnnotation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Annotation)
       return (Annotation) b;
     else
@@ -480,13 +540,20 @@ private Map<String, Object> userData;
   }
   
   public Dosage castToDosage(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Dosage)
       return (Dosage) b;
-    else      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
+    else      
+      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
   }
   
 	
 	public Attachment castToAttachment(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Attachment)
 			return (Attachment) b;
 		else
@@ -494,6 +561,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Identifier castToIdentifier(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Identifier)
 			return (Identifier) b;
 		else
@@ -501,6 +571,9 @@ private Map<String, Object> userData;
 	}
 	
   public CodeableConcept castToCodeableConcept(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof CodeableConcept)
       return (CodeableConcept) b;
     else if (b instanceof Element) {
@@ -514,6 +587,9 @@ private Map<String, Object> userData;
   }
   
   public Population castToPopulation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Population)
       return (Population) b;
     else
@@ -522,6 +598,9 @@ private Map<String, Object> userData;
   
 	
 	public Coding castToCoding(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Coding)
       return (Coding) b;
     else if (b instanceof Element) {
@@ -537,6 +616,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Quantity castToQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Quantity)
 			return (Quantity) b;
 		else
@@ -544,6 +626,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Money castToMoney(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Money)
 			return (Money) b;
 		else
@@ -551,6 +636,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Duration castToDuration(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Duration)
 			return (Duration) b;
 		else
@@ -558,6 +646,9 @@ private Map<String, Object> userData;
 	}
 	
 	public SimpleQuantity castToSimpleQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof SimpleQuantity)
 			return (SimpleQuantity) b;
 		else if (b instanceof Quantity) {
@@ -574,6 +665,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Range castToRange(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Range)
 			return (Range) b;
 		else
@@ -581,6 +675,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Period castToPeriod(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Period)
 			return (Period) b;
 		else
@@ -588,6 +685,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Ratio castToRatio(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Ratio)
 			return (Ratio) b;
 		else
@@ -595,6 +695,9 @@ private Map<String, Object> userData;
 	}
 	
 	public SampledData castToSampledData(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof SampledData)
 			return (SampledData) b;
 		else
@@ -602,6 +705,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Signature castToSignature(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Signature)
 			return (Signature) b;
 		else
@@ -609,6 +715,9 @@ private Map<String, Object> userData;
 	}
 	
 	public HumanName castToHumanName(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof HumanName)
 			return (HumanName) b;
 		else
@@ -616,6 +725,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Address castToAddress(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Address)
 			return (Address) b;
 		else
@@ -623,6 +735,9 @@ private Map<String, Object> userData;
 	}
 	
 	public ContactDetail castToContactDetail(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof ContactDetail)
 			return (ContactDetail) b;
 		else
@@ -630,6 +745,9 @@ private Map<String, Object> userData;
 	}
 
 	public Contributor castToContributor(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Contributor)
 			return (Contributor) b;
 		else
@@ -637,6 +755,9 @@ private Map<String, Object> userData;
 	}
 
 	public UsageContext castToUsageContext(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof UsageContext)
 			return (UsageContext) b;
 		else
@@ -644,6 +765,9 @@ private Map<String, Object> userData;
 	}
 
 	public RelatedArtifact castToRelatedArtifact(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof RelatedArtifact)
 			return (RelatedArtifact) b;
 		else
@@ -651,6 +775,9 @@ private Map<String, Object> userData;
 	}
 
 	public ContactPoint castToContactPoint(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof ContactPoint)
 			return (ContactPoint) b;
 		else
@@ -658,6 +785,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Timing castToTiming(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Timing)
 			return (Timing) b;
 		else
@@ -665,6 +795,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Reference castToReference(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Reference)
 			return (Reference) b;
 		else if (b.isPrimitive() && Utilities.isURL(b.primitiveValue()))
@@ -677,6 +810,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Meta castToMeta(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Meta)
 			return (Meta) b;
 		else
@@ -685,6 +821,9 @@ private Map<String, Object> userData;
 		
 	
   public MarketingStatus castToMarketingStatus(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof MarketingStatus)
       return (MarketingStatus) b;
     else
@@ -692,6 +831,9 @@ private Map<String, Object> userData;
   }
     
   public ProductShelfLife castToProductShelfLife(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ProductShelfLife)
       return (ProductShelfLife) b;
     else
@@ -699,6 +841,9 @@ private Map<String, Object> userData;
   }
     
   public ProdCharacteristic castToProdCharacteristic(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ProdCharacteristic)
       return (ProdCharacteristic) b;
     else
@@ -707,6 +852,9 @@ private Map<String, Object> userData;
     
   
   public SubstanceAmount castToSubstanceAmount(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof SubstanceAmount)
       return (SubstanceAmount) b;
     else
@@ -714,6 +862,9 @@ private Map<String, Object> userData;
   }
     
 	public Extension castToExtension(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Extension)
 			return (Extension) b;
 		else
@@ -721,6 +872,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Resource castToResource(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Resource)
 			return (Resource) b;
 		else
@@ -728,6 +882,9 @@ private Map<String, Object> userData;
 	}
 	
 	public Narrative castToNarrative(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof Narrative)
 			return (Narrative) b;
 		else
@@ -736,6 +893,9 @@ private Map<String, Object> userData;
 	
 	
 	public ElementDefinition castToElementDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof ElementDefinition)
 			return (ElementDefinition) b;
 		else
@@ -743,6 +903,9 @@ private Map<String, Object> userData;
 	}
 
   public DataRequirement castToDataRequirement(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof DataRequirement)
       return (DataRequirement) b;
     else
@@ -750,6 +913,9 @@ private Map<String, Object> userData;
   }
 
   public Expression castToExpression(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Expression)
       return (Expression) b;
     else
@@ -758,6 +924,9 @@ private Map<String, Object> userData;
 
 	
 	public ParameterDefinition castToParameterDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof ParameterDefinition)
 			return (ParameterDefinition) b;
 		else
@@ -765,6 +934,9 @@ private Map<String, Object> userData;
 	}
 
 	public TriggerDefinition castToTriggerDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
 		if (b instanceof TriggerDefinition)
 			return (TriggerDefinition) b;
 		else
@@ -772,6 +944,9 @@ private Map<String, Object> userData;
 	}
 
   public XhtmlNode castToXhtml(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Element) {
       return ((Element) b).getXhtml();
     } else if (b instanceof XhtmlType) {
@@ -787,6 +962,9 @@ private Map<String, Object> userData;
   }
   
   public String castToXhtmlString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Element) {
       return ((Element) b).getValue();
     } else if (b instanceof XhtmlType) {
diff --git a/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/model/TypeConvertor.java b/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/model/TypeConvertor.java
index af44c2fa7..fe2a76457 100644
--- a/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/model/TypeConvertor.java
+++ b/org.hl7.fhir.r4b/src/main/java/org/hl7/fhir/r4b/model/TypeConvertor.java
@@ -15,6 +15,10 @@ public class TypeConvertor {
   // -- converters for property setters
   
   public static DataType castToType(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DataType)
       return (DataType) b;
     else if (b.isMetadataBased())
@@ -25,6 +29,10 @@ public class TypeConvertor {
   
 
   public static BooleanType castToBoolean(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof BooleanType)
       return (BooleanType) b;
     else
@@ -32,6 +40,10 @@ public class TypeConvertor {
   }
   
   public static IntegerType castToInteger(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof IntegerType)
       return (IntegerType) b;
     else
@@ -39,6 +51,10 @@ public class TypeConvertor {
   }
   
   public static Integer64Type castToInteger64(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Integer64Type)
       return (Integer64Type) b;
     else
@@ -46,6 +62,10 @@ public class TypeConvertor {
   }
   
   public static DecimalType castToDecimal(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DecimalType)
       return (DecimalType) b;
     else if (b.hasPrimitiveValue())
@@ -55,6 +75,10 @@ public class TypeConvertor {
   }
   
   public static Base64BinaryType castToBase64Binary(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Base64BinaryType)
       return (Base64BinaryType) b;
     else
@@ -62,6 +86,10 @@ public class TypeConvertor {
   }
   
   public static InstantType castToInstant(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof InstantType)
       return (InstantType) b;
     else
@@ -69,6 +97,10 @@ public class TypeConvertor {
   }
   
   public static StringType castToString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof StringType)
       return (StringType) b;
     else if (b.hasPrimitiveValue())
@@ -78,6 +110,10 @@ public class TypeConvertor {
   }
   
   public static UriType castToUri(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UriType)
       return (UriType) b;
     else if (b.hasPrimitiveValue())
@@ -87,6 +123,10 @@ public class TypeConvertor {
   }
   
   public static UrlType castToUrl(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UrlType)
       return (UrlType) b;
     else if (b.hasPrimitiveValue())
@@ -96,6 +136,10 @@ public class TypeConvertor {
   }
   
   public static CanonicalType castToCanonical(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CanonicalType)
       return (CanonicalType) b;
     else if (b.hasPrimitiveValue())
@@ -105,6 +149,10 @@ public class TypeConvertor {
   }
   
   public static DateType castToDate(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DateType)
       return (DateType) b;
     else if (b.hasPrimitiveValue())
@@ -114,6 +162,10 @@ public class TypeConvertor {
   }
   
   public static DateTimeType castToDateTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DateTimeType)
       return (DateTimeType) b;
     else if (b.fhirType().equals("dateTime"))
@@ -123,6 +175,9 @@ public class TypeConvertor {
   }
   
   public static TimeType castToTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof TimeType)
       return (TimeType) b;
     else
@@ -130,6 +185,9 @@ public class TypeConvertor {
   }
   
   public static CodeType castToCode(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof CodeType)
       return (CodeType) b;
     else if (b.isPrimitive())
@@ -139,6 +197,9 @@ public class TypeConvertor {
   }
   
   public static OidType castToOid(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof OidType)
       return (OidType) b;
     else
@@ -146,6 +207,9 @@ public class TypeConvertor {
   }
   
   public static IdType castToId(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof IdType)
       return (IdType) b;
     else
@@ -153,6 +217,9 @@ public class TypeConvertor {
   }
   
   public static UnsignedIntType castToUnsignedInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof UnsignedIntType)
       return (UnsignedIntType) b;
     else
@@ -160,6 +227,9 @@ public class TypeConvertor {
   }
   
   public static PositiveIntType castToPositiveInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof PositiveIntType)
       return (PositiveIntType) b;
     else
@@ -167,6 +237,9 @@ public class TypeConvertor {
   }
   
   public static MarkdownType castToMarkdown(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof MarkdownType)
       return (MarkdownType) b;
     else if (b.hasPrimitiveValue())
@@ -176,6 +249,9 @@ public class TypeConvertor {
   }
     
   public static Annotation castToAnnotation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Annotation)
       return (Annotation) b;
     else
@@ -183,13 +259,21 @@ public class TypeConvertor {
   }
   
   public static Dosage castToDosage(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Dosage)
       return (Dosage) b;
-    else      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
+    else  
+      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
   }
   
   
   public static Attachment castToAttachment(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Attachment)
       return (Attachment) b;
     else
@@ -197,6 +281,10 @@ public class TypeConvertor {
   }
   
   public static Identifier castToIdentifier(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Identifier)
       return (Identifier) b;
     else
@@ -204,6 +292,10 @@ public class TypeConvertor {
   }
   
   public static CodeableConcept castToCodeableConcept(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CodeableConcept)
       return (CodeableConcept) b;
     else if (b instanceof Element) {
@@ -221,6 +313,10 @@ public class TypeConvertor {
   }
   
   public static CodeableReference castToCodeableReference(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CodeableReference) {
       return (CodeableReference) b;
     } else if (b instanceof CodeType) {
@@ -240,6 +336,10 @@ public class TypeConvertor {
   }
   
   public static Population castToPopulation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Population)
       return (Population) b;
     else
@@ -248,6 +348,10 @@ public class TypeConvertor {
   
   
   public static Coding castToCoding(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Coding)
       return (Coding) b;
     else if (b instanceof Element) {
@@ -270,6 +374,10 @@ public class TypeConvertor {
   }
   
   public static Quantity castToQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Quantity)
       return (Quantity) b;
     else
@@ -277,6 +385,10 @@ public class TypeConvertor {
   }
   
   public static Money castToMoney(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Money)
       return (Money) b;
     else
@@ -284,6 +396,10 @@ public class TypeConvertor {
   }
   
   public static Duration castToDuration(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Duration)
       return (Duration) b;
     else
@@ -291,6 +407,11 @@ public class TypeConvertor {
   }
   
   public static SimpleQuantity castToSimpleQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
+    
     if (b instanceof SimpleQuantity)
       return (SimpleQuantity) b;
     else if (b instanceof Quantity) {
@@ -307,6 +428,10 @@ public class TypeConvertor {
   }
   
   public static Range castToRange(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Range)
       return (Range) b;
     else
@@ -314,6 +439,10 @@ public class TypeConvertor {
   }
   
   public static Period castToPeriod(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Period)
       return (Period) b;
     else
@@ -321,6 +450,10 @@ public class TypeConvertor {
   }
   
   public static Ratio castToRatio(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Ratio)
       return (Ratio) b;
     else
@@ -328,6 +461,11 @@ public class TypeConvertor {
   }
   
   public static SampledData castToSampledData(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
+
     if (b instanceof SampledData)
       return (SampledData) b;
     else
@@ -335,6 +473,9 @@ public class TypeConvertor {
   }
   
   public static Signature castToSignature(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Signature)
       return (Signature) b;
     else
@@ -342,6 +483,9 @@ public class TypeConvertor {
   }
   
   public static HumanName castToHumanName(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof HumanName)
       return (HumanName) b;
     else
@@ -349,6 +493,9 @@ public class TypeConvertor {
   }
   
   public static Address castToAddress(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Address)
       return (Address) b;
     else
@@ -356,6 +503,9 @@ public class TypeConvertor {
   }
   
   public static ContactDetail castToContactDetail(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ContactDetail)
       return (ContactDetail) b;
     else
@@ -363,6 +513,9 @@ public class TypeConvertor {
   }
 
   public static Contributor castToContributor(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Contributor)
       return (Contributor) b;
     else
@@ -370,6 +523,9 @@ public class TypeConvertor {
   }
 
   public static UsageContext castToUsageContext(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof UsageContext)
       return (UsageContext) b;
     else
@@ -377,6 +533,9 @@ public class TypeConvertor {
   }
 
   public static RelatedArtifact castToRelatedArtifact(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof RelatedArtifact)
       return (RelatedArtifact) b;
     else
@@ -384,6 +543,9 @@ public class TypeConvertor {
   }
 
   public static ContactPoint castToContactPoint(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ContactPoint)
       return (ContactPoint) b;
     else
@@ -391,6 +553,9 @@ public class TypeConvertor {
   }
   
   public static Timing castToTiming(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Timing)
       return (Timing) b;
     else
@@ -398,6 +563,9 @@ public class TypeConvertor {
   }
   
   public static Reference castToReference(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Reference)
       return (Reference) b;
     else if (b.isPrimitive() && Utilities.isURL(b.primitiveValue()))
@@ -410,6 +578,9 @@ public class TypeConvertor {
   }
   
   public static Meta castToMeta(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Meta)
       return (Meta) b;
     else
@@ -418,6 +589,9 @@ public class TypeConvertor {
     
   
   public static MarketingStatus castToMarketingStatus(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof MarketingStatus)
       return (MarketingStatus) b;
     else
@@ -425,6 +599,9 @@ public class TypeConvertor {
   }
     
   public static Statistic castToStatistic(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Statistic)
       return (Statistic) b;
     else
@@ -433,6 +610,9 @@ public class TypeConvertor {
    
   
   public static OrderedDistribution castToOrderedDistribution(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof OrderedDistribution)
       return (OrderedDistribution) b;
     else
@@ -440,6 +620,9 @@ public class TypeConvertor {
   }
   
   public static ProductShelfLife castToProductShelfLife(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ProductShelfLife)
       return (ProductShelfLife) b;
     else
@@ -447,6 +630,9 @@ public class TypeConvertor {
   }
     
   public static ProdCharacteristic castToProdCharacteristic(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ProdCharacteristic)
       return (ProdCharacteristic) b;
     else
@@ -455,6 +641,9 @@ public class TypeConvertor {
     
   
   public static SubstanceAmount castToSubstanceAmount(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof SubstanceAmount)
       return (SubstanceAmount) b;
     else
@@ -462,6 +651,9 @@ public class TypeConvertor {
   }
     
   public static Extension castToExtension(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Extension)
       return (Extension) b;
     else
@@ -469,6 +661,9 @@ public class TypeConvertor {
   }
   
   public static Resource castToResource(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Resource)
       return (Resource) b;
     else
@@ -476,6 +671,9 @@ public class TypeConvertor {
   }
   
   public static Narrative castToNarrative(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Narrative)
       return (Narrative) b;
     else
@@ -484,6 +682,9 @@ public class TypeConvertor {
   
   
   public static ElementDefinition castToElementDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ElementDefinition)
       return (ElementDefinition) b;
     else
@@ -491,6 +692,9 @@ public class TypeConvertor {
   }
 
   public static DataRequirement castToDataRequirement(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof DataRequirement)
       return (DataRequirement) b;
     else
@@ -498,6 +702,9 @@ public class TypeConvertor {
   }
 
   public static Expression castToExpression(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Expression)
       return (Expression) b;
     else
@@ -506,6 +713,9 @@ public class TypeConvertor {
 
   
   public static ParameterDefinition castToParameterDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof ParameterDefinition)
       return (ParameterDefinition) b;
     else
@@ -513,6 +723,9 @@ public class TypeConvertor {
   }
 
   public static TriggerDefinition castToTriggerDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof TriggerDefinition)
       return (TriggerDefinition) b;
     else
@@ -520,6 +733,9 @@ public class TypeConvertor {
   }
 
   public static XhtmlNode castToXhtml(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Element) {
       return ((Element) b).getXhtml();
     } else if (b instanceof XhtmlType) {
@@ -535,6 +751,9 @@ public class TypeConvertor {
   }
   
   public static String castToXhtmlString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Element) {
       return ((Element) b).getValue();
     } else if (b instanceof XhtmlType) {
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/TypeConvertor.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/TypeConvertor.java
index f775d8979..10d483951 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/TypeConvertor.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/model/TypeConvertor.java
@@ -15,6 +15,9 @@ public class TypeConvertor {
   // -- converters for property setters
   
   public static DataType castToType(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof DataType)
       return (DataType) b;
     else if (b.isMetadataBased())
@@ -25,6 +28,9 @@ public class TypeConvertor {
   
 
   public static BooleanType castToBoolean(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof BooleanType)
       return (BooleanType) b;
     else
@@ -32,6 +38,9 @@ public class TypeConvertor {
   }
   
   public static IntegerType castToInteger(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof IntegerType)
       return (IntegerType) b;
     else
@@ -39,6 +48,9 @@ public class TypeConvertor {
   }
   
   public static Integer64Type castToInteger64(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Integer64Type)
       return (Integer64Type) b;
     else
@@ -46,6 +58,9 @@ public class TypeConvertor {
   }
   
   public static DecimalType castToDecimal(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof DecimalType)
       return (DecimalType) b;
     else if (b.hasPrimitiveValue())
@@ -55,6 +70,9 @@ public class TypeConvertor {
   }
   
   public static Base64BinaryType castToBase64Binary(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof Base64BinaryType)
       return (Base64BinaryType) b;
     else
@@ -62,6 +80,9 @@ public class TypeConvertor {
   }
   
   public static InstantType castToInstant(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
     if (b instanceof InstantType)
       return (InstantType) b;
     else
@@ -69,6 +90,10 @@ public class TypeConvertor {
   }
   
   public static StringType castToString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof StringType)
       return (StringType) b;
     else if (b.hasPrimitiveValue())
@@ -78,6 +103,10 @@ public class TypeConvertor {
   }
   
   public static UriType castToUri(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UriType)
       return (UriType) b;
     else if (b.hasPrimitiveValue())
@@ -87,6 +116,10 @@ public class TypeConvertor {
   }
   
   public static UrlType castToUrl(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UrlType)
       return (UrlType) b;
     else if (b.hasPrimitiveValue())
@@ -96,6 +129,10 @@ public class TypeConvertor {
   }
   
   public static CanonicalType castToCanonical(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CanonicalType)
       return (CanonicalType) b;
     else if (b.hasPrimitiveValue())
@@ -105,6 +142,10 @@ public class TypeConvertor {
   }
   
   public static DateType castToDate(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DateType)
       return (DateType) b;
     else if (b.hasPrimitiveValue())
@@ -114,6 +155,10 @@ public class TypeConvertor {
   }
   
   public static DateTimeType castToDateTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DateTimeType)
       return (DateTimeType) b;
     else if (b.fhirType().equals("dateTime"))
@@ -123,6 +168,10 @@ public class TypeConvertor {
   }
   
   public static TimeType castToTime(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof TimeType)
       return (TimeType) b;
     else
@@ -130,6 +179,10 @@ public class TypeConvertor {
   }
   
   public static CodeType castToCode(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CodeType)
       return (CodeType) b;
     else if (b.isPrimitive())
@@ -139,6 +192,10 @@ public class TypeConvertor {
   }
   
   public static OidType castToOid(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof OidType)
       return (OidType) b;
     else
@@ -146,6 +203,10 @@ public class TypeConvertor {
   }
   
   public static IdType castToId(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof IdType)
       return (IdType) b;
     else
@@ -153,6 +214,10 @@ public class TypeConvertor {
   }
   
   public static UnsignedIntType castToUnsignedInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UnsignedIntType)
       return (UnsignedIntType) b;
     else
@@ -160,6 +225,10 @@ public class TypeConvertor {
   }
   
   public static PositiveIntType castToPositiveInt(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof PositiveIntType)
       return (PositiveIntType) b;
     else
@@ -167,6 +236,10 @@ public class TypeConvertor {
   }
   
   public static MarkdownType castToMarkdown(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof MarkdownType)
       return (MarkdownType) b;
     else if (b.hasPrimitiveValue())
@@ -176,6 +249,10 @@ public class TypeConvertor {
   }
     
   public static Annotation castToAnnotation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Annotation)
       return (Annotation) b;
     else
@@ -183,13 +260,22 @@ public class TypeConvertor {
   }
   
   public static Dosage castToDosage(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Dosage)
       return (Dosage) b;
-    else      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
+    else      
+      throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to an DosageInstruction");
   }
   
   
   public static Attachment castToAttachment(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Attachment)
       return (Attachment) b;
     else
@@ -197,6 +283,10 @@ public class TypeConvertor {
   }
   
   public static Identifier castToIdentifier(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Identifier)
       return (Identifier) b;
     else
@@ -204,6 +294,10 @@ public class TypeConvertor {
   }
   
   public static CodeableConcept castToCodeableConcept(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CodeableConcept)
       return (CodeableConcept) b;
     else if (b instanceof Element) {
@@ -221,6 +315,10 @@ public class TypeConvertor {
   }
   
   public static CodeableReference castToCodeableReference(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof CodeableReference) {
       return (CodeableReference) b;
     } else if (b instanceof CodeType) {
@@ -240,6 +338,10 @@ public class TypeConvertor {
   }
   
   public static Population castToPopulation(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Population)
       return (Population) b;
     else
@@ -248,6 +350,10 @@ public class TypeConvertor {
   
   
   public static Coding castToCoding(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Coding)
       return (Coding) b;
     else if (b instanceof Element) {
@@ -270,6 +376,10 @@ public class TypeConvertor {
   }
   
   public static Quantity castToQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Quantity)
       return (Quantity) b;
     else
@@ -277,6 +387,10 @@ public class TypeConvertor {
   }
   
   public static Count castToCount(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Count)
       return (Count) b;
     else
@@ -284,6 +398,10 @@ public class TypeConvertor {
   }
   
   public static Money castToMoney(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Money)
       return (Money) b;
     else
@@ -291,6 +409,10 @@ public class TypeConvertor {
   }
   
   public static Duration castToDuration(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Duration)
       return (Duration) b;
     else
@@ -298,6 +420,10 @@ public class TypeConvertor {
   }
   
   public static SimpleQuantity castToSimpleQuantity(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof SimpleQuantity)
       return (SimpleQuantity) b;
     else if (b instanceof Quantity) {
@@ -314,6 +440,10 @@ public class TypeConvertor {
   }
   
   public static Range castToRange(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Range)
       return (Range) b;
     else
@@ -321,6 +451,10 @@ public class TypeConvertor {
   }
   
   public static Period castToPeriod(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Period)
       return (Period) b;
     else
@@ -328,6 +462,10 @@ public class TypeConvertor {
   }
   
   public static Ratio castToRatio(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Ratio)
       return (Ratio) b;
     else
@@ -335,6 +473,10 @@ public class TypeConvertor {
   }
   
   public static SampledData castToSampledData(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof SampledData)
       return (SampledData) b;
     else
@@ -342,6 +484,10 @@ public class TypeConvertor {
   }
   
   public static Signature castToSignature(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Signature)
       return (Signature) b;
     else
@@ -349,6 +495,10 @@ public class TypeConvertor {
   }
   
   public static HumanName castToHumanName(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof HumanName)
       return (HumanName) b;
     else
@@ -356,6 +506,10 @@ public class TypeConvertor {
   }
   
   public static Address castToAddress(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Address)
       return (Address) b;
     else
@@ -363,6 +517,10 @@ public class TypeConvertor {
   }
   
   public static ContactDetail castToContactDetail(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ContactDetail)
       return (ContactDetail) b;
     else
@@ -370,6 +528,10 @@ public class TypeConvertor {
   }
 
   public static Contributor castToContributor(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Contributor)
       return (Contributor) b;
     else
@@ -377,6 +539,10 @@ public class TypeConvertor {
   }
 
   public static UsageContext castToUsageContext(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof UsageContext)
       return (UsageContext) b;
     else
@@ -384,6 +550,10 @@ public class TypeConvertor {
   }
 
   public static RelatedArtifact castToRelatedArtifact(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof RelatedArtifact)
       return (RelatedArtifact) b;
     else
@@ -391,6 +561,10 @@ public class TypeConvertor {
   }
 
   public static ContactPoint castToContactPoint(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ContactPoint)
       return (ContactPoint) b;
     else
@@ -398,6 +572,10 @@ public class TypeConvertor {
   }
   
   public static Timing castToTiming(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Timing)
       return (Timing) b;
     else
@@ -405,6 +583,10 @@ public class TypeConvertor {
   }
   
   public static Reference castToReference(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Reference)
       return (Reference) b;
     else if (b.isPrimitive() && Utilities.isURL(b.primitiveValue()))
@@ -417,6 +599,10 @@ public class TypeConvertor {
   }
   
   public static Meta castToMeta(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Meta)
       return (Meta) b;
     else
@@ -425,6 +611,10 @@ public class TypeConvertor {
     
   
   public static MarketingStatus castToMarketingStatus(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof MarketingStatus)
       return (MarketingStatus) b;
     else
@@ -432,6 +622,10 @@ public class TypeConvertor {
   }
     
   public static Statistic castToStatistic(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Statistic)
       return (Statistic) b;
     else
@@ -440,13 +634,21 @@ public class TypeConvertor {
    
   
   public static OrderedDistribution castToOrderedDistribution(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof OrderedDistribution)
       return (OrderedDistribution) b;
     else
       throw new FHIRException("Unable to convert a "+b.getClass().getName()+" to a OrderedDistribution");
   }
   
-  public static ProductShelfLife castToProductShelfLife(Base b) throws FHIRException {
+  public static ProductShelfLife castToProductShelfLife(Base b) throws FHIRException {   
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ProductShelfLife)
       return (ProductShelfLife) b;
     else
@@ -454,6 +656,10 @@ public class TypeConvertor {
   }
     
   public static ProdCharacteristic castToProdCharacteristic(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ProdCharacteristic)
       return (ProdCharacteristic) b;
     else
@@ -462,6 +668,10 @@ public class TypeConvertor {
     
   
   public static SubstanceAmount castToSubstanceAmount(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof SubstanceAmount)
       return (SubstanceAmount) b;
     else
@@ -469,6 +679,10 @@ public class TypeConvertor {
   }
     
   public static Extension castToExtension(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Extension)
       return (Extension) b;
     else
@@ -476,6 +690,10 @@ public class TypeConvertor {
   }
   
   public static Resource castToResource(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Resource)
       return (Resource) b;
     else
@@ -483,6 +701,10 @@ public class TypeConvertor {
   }
   
   public static Narrative castToNarrative(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Narrative)
       return (Narrative) b;
     else
@@ -491,6 +713,10 @@ public class TypeConvertor {
   
   
   public static ElementDefinition castToElementDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ElementDefinition)
       return (ElementDefinition) b;
     else
@@ -498,6 +724,10 @@ public class TypeConvertor {
   }
 
   public static DataRequirement castToDataRequirement(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof DataRequirement)
       return (DataRequirement) b;
     else
@@ -505,6 +735,10 @@ public class TypeConvertor {
   }
 
   public static Expression castToExpression(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Expression)
       return (Expression) b;
     else
@@ -513,6 +747,10 @@ public class TypeConvertor {
 
   
   public static ParameterDefinition castToParameterDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ParameterDefinition)
       return (ParameterDefinition) b;
     else
@@ -520,6 +758,10 @@ public class TypeConvertor {
   }
 
   public static TriggerDefinition castToTriggerDefinition(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof TriggerDefinition)
       return (TriggerDefinition) b;
     else
@@ -527,6 +769,10 @@ public class TypeConvertor {
   }
   
   public static ExtendedContactDetail castToExtendedContactDetail(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof ExtendedContactDetail)
       return (ExtendedContactDetail) b;
     else
@@ -537,6 +783,10 @@ public class TypeConvertor {
   
 
   public static XhtmlNode castToXhtml(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Element) {
       return ((Element) b).getXhtml();
     } else if (b instanceof XhtmlType) {
@@ -552,6 +802,10 @@ public class TypeConvertor {
   }
   
   public static String castToXhtmlString(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Element) {
       return ((Element) b).getValue();
     } else if (b instanceof XhtmlType) {
@@ -568,6 +822,10 @@ public class TypeConvertor {
 
 
   public static VirtualServiceDetail castToVirtualServiceDetail(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof VirtualServiceDetail)
       return (VirtualServiceDetail) b;
     else
@@ -576,6 +834,10 @@ public class TypeConvertor {
 
 
   public static Availability castToAvailability(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof Availability)
       return (Availability) b;
     else
@@ -584,6 +846,10 @@ public class TypeConvertor {
 
 
   public static MonetaryComponent castToMonetaryComponent(Base b) throws FHIRException {
+    if (b == null) {
+      return null;
+    }
+
     if (b instanceof MonetaryComponent)
       return (MonetaryComponent) b;
     else
diff --git a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/renderers/StructureDefinitionRenderer.java b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/renderers/StructureDefinitionRenderer.java
index 619d5e960..32125968a 100644
--- a/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/renderers/StructureDefinitionRenderer.java
+++ b/org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/renderers/StructureDefinitionRenderer.java
@@ -382,7 +382,7 @@ public class StructureDefinitionRenderer extends ResourceRenderer {
   
   public void scanBindings(Set<String> cols, List<ElementDefinition> list, ElementDefinition ed) {
     if (ed.hasBinding()) {
-      if (ed.getBinding().hasValueSet()) {
+      if (ed.getBinding().hasValueSet() && ed.getBinding().hasStrength()) {
         switch (ed.getBinding().getStrength()) {
         case EXAMPLE:
           cols.add("example");
@@ -770,7 +770,7 @@ public class StructureDefinitionRenderer extends ResourceRenderer {
     List<ElementDefinitionBindingAdditionalComponent> res = new ArrayList<>();
     if (element.hasBinding()) {
       ElementDefinitionBindingComponent b = element.getBinding();
-      if (type.equals(b.getStrength().toCode())) {
+      if (b.hasStrength() && type.equals(b.getStrength().toCode())) {
         ElementDefinitionBindingAdditionalComponent ab = new ElementDefinitionBindingAdditionalComponent();
         res.add(ab.setAny(false).setDocumentation(b.getDescription()).setValueSet(b.getValueSet()));
       }
@@ -990,6 +990,9 @@ public class StructureDefinitionRenderer extends ResourceRenderer {
   }
 
   private Row makeChoiceElementRow(HierarchicalTableGenerator gen, Row prow, ElementChoiceGroup grp, ElementDefinition parent, boolean isConstraintMode) {
+    if (context.getStructureMode() != StructureDefinitionRendererMode.SUMMARY) {
+      return prow;
+    }
     Row row = gen.new Row();
     row.setAnchor(parent.getPath()+"-"+grp.getName());
     row.setColor(context.getProfileUtilities().getRowColor(parent, isConstraintMode));