Fix unresolved sticky class GC roots

profiler/lib.profiler/src/org/netbeans/lib/profiler/heap/HprofGCRoots.java

@@ -93,7 +93,10 @@ GCRoot getGCRoot(Long instanceId) {
                 heap.getGCRoots();
                 roots = new HashMap<>();
                 for (GCRoot r : getGCRoots()) {
-                    roots.put(r.getInstance().getInstanceId(), r);
+                    Instance instance = r.getInstance();
+                    if (instance != null) {
+                        roots.put(instance.getInstanceId(), r);
+                    }
                 }
                 gcRoots = roots;
             } else {

profiler/lib.profiler/test/unit/src/org/netbeans/lib/profiler/heap/HeapSegmentTest.java

@@ -31,6 +31,7 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
 import org.junit.Test;
 import org.netbeans.lib.profiler.heap.HeapUtils.HprofGenerator;
 
@@ -45,6 +46,29 @@ public void singleObjectMultipleSegments() throws IOException {
         singleObject(true);
     }
 
+    @Test
+    public void unresolvedStickyClassRootDoesNotBreakGCRootLookup() throws IOException {
+        File mydump = File.createTempFile("mydump", ".hprof");
+        try (HprofGenerator gen = new HprofGenerator(new FileOutputStream(mydump))) {
+            gen.writeHeapSegment(new HprofGenerator.Generator<HprofGenerator.HeapSegment>() {
+                @Override
+                public void generate(HprofGenerator.HeapSegment seg) throws IOException {
+                    seg.newClass("com.oracle.svm.core.heap.heapImpl.DiscoverableReference")
+                            .addField("rawReferent", Object.class)
+                            .dumpClass();
+                    HprofGenerator.ClassInstance clazz = seg.newClass("text.HelloWorld").dumpClass();
+                    seg.dumpStickyClassRoot(clazz);
+                    seg.dumpInstance(clazz);
+                }
+            }, true);
+        }
+
+        Heap heap = HeapFactory.createHeap(mydump);
+        assertEquals("One unresolved sticky class root", 1, heap.getGCRoots().size());
+        Instance instance = (Instance) heap.getJavaClassByName("text.HelloWorld").getInstances().iterator().next();
+        assertNull("Non-root instance", heap.getGCRoot(instance));
+    }
+
     private static void singleObject(boolean flush) throws IOException {
         File mydump = File.createTempFile("mydump", ".hprof");
         Heap heap = generateSampleDump(mydump, flush);

profiler/lib.profiler/test/unit/src/org/netbeans/lib/profiler/heap/HeapUtils.java

@@ -170,6 +170,11 @@ public int dumpPrimitive(Object obj) throws IOException {
                 return instanceId;
             }
 
+            public void dumpStickyClassRoot(ClassInstance clazz) throws IOException {
+                heap.writeByte(0x05);
+                heap.writeInt(clazz.id);
+            }
+
             public final class ThreadBuilder {
 
                 private String groupName;