Correctly handle an unresolved object type

Author: jisedlac

visualvm/heapviewer.truffle/src/org/graalvm/visualvm/heapviewer/truffle/dynamicobject/DynamicObject.java

@@ -155,7 +155,10 @@ public static Instance getShape(Instance instance) {
 
     @Override
     public String getType(Heap heap) {
-        if (type == null) type = computeType(heap);
+        if (type == null) {
+            type = computeType(heap);
+            if (type == null) type = "<unknown type>"; // NOI18N
+        }
         return type;
     }
 

visualvm/heapviewer.truffle/src/org/graalvm/visualvm/heapviewer/truffle/lang/python/PythonObject.java

@@ -141,7 +141,10 @@ public Instance getInstance() {
 
     @Override
     public String getType(Heap heap) {
-        if (type == null) type = DetailsUtils.getInstanceString(pythonClass, null);
+        if (type == null) {
+            type = DetailsUtils.getInstanceString(pythonClass, null);
+            if (type == null) type = "<unknown type>"; // NOI18N
+        }
         return type;
     }