NPE fixes

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/elementmodel/Element.java

@@ -1110,6 +1110,20 @@ public class Element extends Base implements NamedItem {
     return null;
   }
 
+  public String getExtensionString(String url) {
+    if (children != null) {
+      for (Element child : children) {
+        if (extensionList.contains(child.getName())) {
+          String u = child.getChildValue("url");
+          if (url.equals(u)) {
+            return child.getNamedChildValue("value");
+          }
+        }
+      }
+    }
+    return null;
+  }
+
   public List<Element> getExtensions(String url) {
     List<Element> list = new ArrayList<>();
     if (children != null) {

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/fhirpath/FHIRPathEngine.java

@@ -6572,8 +6572,13 @@ public class FHIRPathEngine {
   }
 
   private ElementDefinitionMatch getElementDefinitionById(StructureDefinition sd, String ref) {
-    if (ref.startsWith(sd.getUrl()+"#")) {
-      ref = ref.replace(sd.getUrl()+"#", "#"); 
+    StructureDefinition sdt = sd; 
+    while (sdt != null) {
+      if (ref.startsWith(sdt.getUrl()+"#")) {
+        ref = ref.replace(sdt.getUrl()+"#", "#");
+        break;
+      }
+      sdt = worker.fetchResource(StructureDefinition.class, sdt.getBaseDefinition());
     }
     for (ElementDefinition ed : sd.getSnapshot().getElement()) {
       if (ref.equals("#"+ed.getId())) {

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/renderers/BundleRenderer.java

@@ -289,7 +289,7 @@ public class BundleRenderer extends ResourceRenderer {
   
   public static boolean allEntriesAreHistoryProvenance(List<ResourceWrapper> entries) throws UnsupportedEncodingException, FHIRException, IOException {
     for (ResourceWrapper be : entries) {
-      if (!"Provenance".equals(be.child("resource").fhirType())) {
+      if (!be.has("child") || !"Provenance".equals(be.child("resource").fhirType())) {
         return false;
       }
     }