diff --git a/hapi-fhir-base/src/main/java/ca/uhn/fhir/context/ModelScanner.java b/hapi-fhir-base/src/main/java/ca/uhn/fhir/context/ModelScanner.java
index 6cce600e631..e5554769f37 100644
--- a/hapi-fhir-base/src/main/java/ca/uhn/fhir/context/ModelScanner.java
+++ b/hapi-fhir-base/src/main/java/ca/uhn/fhir/context/ModelScanner.java
@@ -29,6 +29,7 @@ import ca.uhn.fhir.rest.api.RestSearchParameterTypeEnum;
 import ca.uhn.fhir.util.ReflectionUtil;
 import org.hl7.fhir.instance.model.api.*;
 
+import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.io.InputStream;
 import java.lang.annotation.Annotation;
@@ -44,56 +45,47 @@ import static org.apache.commons.lang3.StringUtils.isBlank;
 class ModelScanner {
 	private static final org.slf4j.Logger ourLog = org.slf4j.LoggerFactory.getLogger(ModelScanner.class);
 
-	private Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> myClassToElementDefinitions = new HashMap<Class<? extends IBase>, BaseRuntimeElementDefinition<?>>();
+	private Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> myClassToElementDefinitions = new HashMap<>();
 	private FhirContext myContext;
-	private Map<String, RuntimeResourceDefinition> myIdToResourceDefinition = new HashMap<String, RuntimeResourceDefinition>();
-	private Map<String, BaseRuntimeElementDefinition<?>> myNameToElementDefinitions = new HashMap<String, BaseRuntimeElementDefinition<?>>();
-	private Map<String, RuntimeResourceDefinition> myNameToResourceDefinitions = new HashMap<String, RuntimeResourceDefinition>();
-	private Map<String, Class<? extends IBaseResource>> myNameToResourceType = new HashMap<String, Class<? extends IBaseResource>>();
+	private Map<String, RuntimeResourceDefinition> myIdToResourceDefinition = new HashMap<>();
+	private Map<String, BaseRuntimeElementDefinition<?>> myNameToElementDefinitions = new HashMap<>();
+	private Map<String, RuntimeResourceDefinition> myNameToResourceDefinitions = new HashMap<>();
+	private Map<String, Class<? extends IBaseResource>> myNameToResourceType = new HashMap<>();
 	private RuntimeChildUndeclaredExtensionDefinition myRuntimeChildUndeclaredExtensionDefinition;
-	private Set<Class<? extends IBase>> myScanAlso = new HashSet<Class<? extends IBase>>();
+	private Set<Class<? extends IBase>> myScanAlso = new HashSet<>();
 	private FhirVersionEnum myVersion;
 
 	private Set<Class<? extends IBase>> myVersionTypes;
 
 	ModelScanner(FhirContext theContext, FhirVersionEnum theVersion, Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> theExistingDefinitions,
-					 Collection<Class<? extends IBase>> theResourceTypes) throws ConfigurationException {
+					 @Nonnull Collection<Class<? extends IBase>> theResourceTypes) throws ConfigurationException {
 		myContext = theContext;
 		myVersion = theVersion;
-		Set<Class<? extends IBase>> toScan;
-		if (theResourceTypes != null) {
-			toScan = new HashSet<Class<? extends IBase>>(theResourceTypes);
-		} else {
-			toScan = new HashSet<Class<? extends IBase>>();
-		}
+		Set<Class<? extends IBase>> toScan = new HashSet<>(theResourceTypes);
 		init(theExistingDefinitions, toScan);
 	}
 
-	public Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> getClassToElementDefinitions() {
+	Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> getClassToElementDefinitions() {
 		return myClassToElementDefinitions;
 	}
 
-	public Map<String, RuntimeResourceDefinition> getIdToResourceDefinition() {
+	Map<String, RuntimeResourceDefinition> getIdToResourceDefinition() {
 		return myIdToResourceDefinition;
 	}
 
-	public Map<String, BaseRuntimeElementDefinition<?>> getNameToElementDefinitions() {
+	Map<String, BaseRuntimeElementDefinition<?>> getNameToElementDefinitions() {
 		return myNameToElementDefinitions;
 	}
 
-	public Map<String, RuntimeResourceDefinition> getNameToResourceDefinition() {
+	Map<String, RuntimeResourceDefinition> getNameToResourceDefinition() {
 		return myNameToResourceDefinitions;
 	}
 
-	public Map<String, RuntimeResourceDefinition> getNameToResourceDefinitions() {
-		return (myNameToResourceDefinitions);
-	}
-
-	public Map<String, Class<? extends IBaseResource>> getNameToResourceType() {
+	Map<String, Class<? extends IBaseResource>> getNameToResourceType() {
 		return myNameToResourceType;
 	}
 
-	public RuntimeChildUndeclaredExtensionDefinition getRuntimeChildUndeclaredExtensionDefinition() {
+	RuntimeChildUndeclaredExtensionDefinition getRuntimeChildUndeclaredExtensionDefinition() {
 		return myRuntimeChildUndeclaredExtensionDefinition;
 	}
 
@@ -145,11 +137,10 @@ class ModelScanner {
 	}
 
 	private boolean isStandardType(Class<? extends IBase> theClass) {
-		boolean retVal = myVersionTypes.contains(theClass);
-		return retVal;
+		return myVersionTypes.contains(theClass);
 	}
 
-	private void scan(Class<? extends IBase> theClass) throws ConfigurationException {
+	void scan(Class<? extends IBase> theClass) throws ConfigurationException {
 		BaseRuntimeElementDefinition<?> existingDef = myClassToElementDefinitions.get(theClass);
 		if (existingDef != null) {
 			return;
@@ -204,9 +195,6 @@ class ModelScanner {
 		ourLog.debug("Scanning resource block class: {}", theClass.getName());
 
 		String resourceName = theClass.getCanonicalName();
-		if (isBlank(resourceName)) {
-			throw new ConfigurationException("Block type @" + Block.class.getSimpleName() + " annotation contains no name: " + theClass.getCanonicalName());
-		}
 
 		// Just in case someone messes up when upgrading from DSTU2
 		if (myContext.getVersion().getVersion().isEqualOrNewerThan(FhirVersionEnum.DSTU3)) {
@@ -341,14 +329,14 @@ class ModelScanner {
 
 	private void scanResourceForSearchParams(Class<? extends IBaseResource> theClass, RuntimeResourceDefinition theResourceDef) {
 
-		Map<String, RuntimeSearchParam> nameToParam = new HashMap<String, RuntimeSearchParam>();
-		Map<Field, SearchParamDefinition> compositeFields = new LinkedHashMap<Field, SearchParamDefinition>();
+		Map<String, RuntimeSearchParam> nameToParam = new HashMap<>();
+		Map<Field, SearchParamDefinition> compositeFields = new LinkedHashMap<>();
 
 		/*
 		 * Make sure we pick up fields in interfaces too.. This ensures that we
 		 * grab the _id field which generally gets picked up via interface
 		 */
-		Set<Field> fields = new HashSet<Field>(Arrays.asList(theClass.getFields()));
+		Set<Field> fields = new HashSet<>(Arrays.asList(theClass.getFields()));
 		Class<?> nextClass = theClass;
 		do {
 			for (Class<?> nextInterface : nextClass.getInterfaces()) {
@@ -400,12 +388,12 @@ class ModelScanner {
 		for (Entry<Field, SearchParamDefinition> nextEntry : compositeFields.entrySet()) {
 			SearchParamDefinition searchParam = nextEntry.getValue();
 
-			List<RuntimeSearchParam> compositeOf = new ArrayList<RuntimeSearchParam>();
+			List<RuntimeSearchParam> compositeOf = new ArrayList<>();
 			for (String nextName : searchParam.compositeOf()) {
 				RuntimeSearchParam param = nameToParam.get(nextName);
 				if (param == null) {
 					ourLog.warn("Search parameter {}.{} declares that it is a composite with compositeOf value '{}' but that is not a valid parametr name itself. Valid values are: {}",
-						new Object[]{theResourceDef.getName(), searchParam.name(), nextName, nameToParam.keySet()});
+						theResourceDef.getName(), searchParam.name(), nextName, nameToParam.keySet());
 					continue;
 				}
 				compositeOf.add(param);
@@ -417,7 +405,7 @@ class ModelScanner {
 	}
 
 	private Set<String> toTargetList(Class<? extends IBaseResource>[] theTarget) {
-		HashSet<String> retVal = new HashSet<String>();
+		HashSet<String> retVal = new HashSet<>();
 
 		for (Class<? extends IBaseResource> nextType : theTarget) {
 			ResourceDef resourceDef = nextType.getAnnotation(ResourceDef.class);
@@ -486,7 +474,7 @@ class ModelScanner {
 	}
 
 	static Set<Class<? extends IBase>> scanVersionPropertyFile(Set<Class<? extends IBase>> theDatatypes, Map<String, Class<? extends IBaseResource>> theResourceTypes, FhirVersionEnum theVersion, Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> theExistingElementDefinitions) {
-		Set<Class<? extends IBase>> retVal = new HashSet<Class<? extends IBase>>();
+		Set<Class<? extends IBase>> retVal = new HashSet<>();
 
 		try (InputStream str = theVersion.getVersionImplementation().getFhirVersionPropertiesFile()) {
 			Properties prop = new Properties();
diff --git a/hapi-fhir-structures-dstu3/src/test/java/ca/uhn/fhir/context/ModelScannerDstu3Test.java b/hapi-fhir-structures-dstu3/src/test/java/ca/uhn/fhir/context/ModelScannerDstu3Test.java
index 198ef7b9b8d..c365df459c3 100644
--- a/hapi-fhir-structures-dstu3/src/test/java/ca/uhn/fhir/context/ModelScannerDstu3Test.java
+++ b/hapi-fhir-structures-dstu3/src/test/java/ca/uhn/fhir/context/ModelScannerDstu3Test.java
@@ -1,17 +1,19 @@
 package ca.uhn.fhir.context;
 
-import ca.uhn.fhir.model.api.annotation.*;
 import ca.uhn.fhir.model.api.annotation.Extension;
+import ca.uhn.fhir.model.api.annotation.*;
 import ca.uhn.fhir.model.primitive.StringDt;
 import ca.uhn.fhir.parser.DataFormatException;
 import ca.uhn.fhir.util.TestUtil;
 import org.hl7.fhir.dstu3.model.*;
+import org.hl7.fhir.instance.model.api.IBase;
 import org.junit.AfterClass;
 import org.junit.Ignore;
 import org.junit.Test;
 
-import java.util.List;
+import java.util.*;
 
+import static org.hamcrest.Matchers.contains;
 import static org.junit.Assert.*;
 
 public class ModelScannerDstu3Test {
@@ -149,6 +151,73 @@ public class ModelScannerDstu3Test {
 		}
 	}
 
+	@Test
+	public void testScanDuplicate() {
+		FhirContext ctx = FhirContext.forDstu3();
+		FhirVersionEnum version = FhirVersionEnum.DSTU3;
+		Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> definitions = new HashMap<>();
+		Collection<Class<? extends IBase>> resourceTypes = new ArrayList<>();
+		resourceTypes.add(Patient.class);
+		ModelScanner scanner = new ModelScanner(ctx, version, definitions, resourceTypes);
+		assertThat(resourceTypes, contains(Patient.class));
+
+		// Extra scans don't do anything
+		scanner.scan(Patient.class);
+		scanner.scan(Patient.class);
+		assertThat(resourceTypes, contains(Patient.class));
+	}
+
+	@Test
+	public void testScanInvalidResource() {
+		FhirContext ctx = FhirContext.forDstu3();
+		FhirVersionEnum version = FhirVersionEnum.DSTU3;
+		Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> definitions = new HashMap<>();
+		Collection<Class<? extends IBase>> resourceTypes = new ArrayList<>();
+		ModelScanner scanner = new ModelScanner(ctx, version, definitions, resourceTypes);
+
+		try {
+			scanner.scan(BadPatient.class);
+			fail();
+		} catch (ConfigurationException e) {
+			assertEquals("Resource type contains a @ResourceDef annotation but does not implement ca.uhn.fhir.model.api.IResource: ca.uhn.fhir.context.ModelScannerDstu3Test.BadPatient", e.getMessage());
+		}
+	}
+
+	@Test
+	public void testScanInvalidType() {
+		FhirContext ctx = FhirContext.forDstu3();
+		FhirVersionEnum version = FhirVersionEnum.DSTU3;
+		Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> definitions = new HashMap<>();
+		Collection<Class<? extends IBase>> resourceTypes = new ArrayList<>();
+		ModelScanner scanner = new ModelScanner(ctx, version, definitions, resourceTypes);
+
+		Class clazz = String.class;
+		try {
+			scanner.scan(clazz);
+			fail();
+		} catch (ConfigurationException e) {
+			assertEquals("Resource class[java.lang.String] does not contain any valid HAPI-FHIR annotations", e.getMessage());
+		}
+	}
+
+	@Test
+	public void testScanInvalidBlock() {
+
+
+		FhirContext ctx = FhirContext.forDstu3();
+		FhirVersionEnum version = FhirVersionEnum.DSTU3;
+		Map<Class<? extends IBase>, BaseRuntimeElementDefinition<?>> definitions = new HashMap<>();
+		Collection<Class<? extends IBase>> resourceTypes = new ArrayList<>();
+		ModelScanner scanner = new ModelScanner(ctx, version, definitions, resourceTypes);
+
+		try {
+			scanner.scan(BadPatient.BadBlock.class);
+			fail();
+		} catch (ConfigurationException e) {
+			assertEquals("Type contains a @Block annotation but does not implement ca.uhn.fhir.model.api.IResourceBlock: ca.uhn.fhir.context.ModelScannerDstu3Test.BadPatient.BadBlock", e.getMessage());
+		}
+	}
+
 	class NoResourceDef extends Patient {
 		@SearchParamDefinition(name = "foo", path = "Patient.telecom", type = "bar")
 		public static final String SP_TELECOM = "foo";
@@ -156,6 +225,78 @@ public class ModelScannerDstu3Test {
 
 	}
 
+	@ResourceDef(name = "Patient")
+	public static class BadPatient implements IBase {
+
+		@Child(name = "badBlock")
+		private BadBlock myChild;
+
+		@Override
+		public boolean isEmpty() {
+			return false;
+		}
+
+		@Override
+		public boolean hasFormatComment() {
+			return false;
+		}
+
+		@Override
+		public List<String> getFormatCommentsPre() {
+			return null;
+		}
+
+		@Override
+		public List<String> getFormatCommentsPost() {
+			return null;
+		}
+
+		@Override
+		public Object getUserData(String theName) {
+			return null;
+		}
+
+		@Override
+		public void setUserData(String theName, Object theValue) {
+
+		}
+
+		@Block
+		public static class BadBlock implements IBase {
+
+			@Override
+			public boolean isEmpty() {
+				return false;
+			}
+
+			@Override
+			public boolean hasFormatComment() {
+				return false;
+			}
+
+			@Override
+			public List<String> getFormatCommentsPre() {
+				return null;
+			}
+
+			@Override
+			public List<String> getFormatCommentsPost() {
+				return null;
+			}
+
+			@Override
+			public Object getUserData(String theName) {
+				return null;
+			}
+
+			@Override
+			public void setUserData(String theName, Object theValue) {
+
+			}
+		}
+
+	}
+
 	@ResourceDef(name = "Patient")
 	public static class CompartmentForNonReferenceParam extends Patient {
 		@SearchParamDefinition(name = "foo", path = "Patient.telecom", type = "string", providesMembershipIn = {@Compartment(name = "Patient"), @Compartment(name = "Device")})