This was discovered when merging JDK-8365932 into the leyden-premain branch, where we can have a heap root whose value is null:

https://github.com/openjdk/leyden/blob/b4058abd25e784106726da3504815d651e340af5/src/hotspot/share/cds/heapShared.cpp#L140

static ArchivableStaticFieldInfo archive_subgraph_entry_fields[] = {
  [...]
  {"java/lang/reflect/Proxy$ProxyBuilder", "archivedData"}, // FIXME -- requires AOTClassLinking
 
The root for Proxy$ProxyBuilder::archivedData is null when AOTClassLinking is disabled during AOT assembly phase.

When running with such an AOT cache, the VM crashes:

V [libjvm.so+0x73b698] AOTStreamedHeapLoader::heap_object_for_object_index(int)+0x28 (aotStreamedHeapLoader.cpp:128)
V [libjvm.so+0x745eca] AOTStreamedHeapLoader::TracingObjectLoader::materialize_object(int, Stack<AOTHeapTraversalEntry, (MemTag)13>&, JavaThread*)+0x11a (aotStreamedHeapLoader.cpp:479)
V [libjvm.so+0x74670b] AOTStreamedHeapLoader::TracingObjectLoader::materialize_object_transitive(int, Stack<AOTHeapTraversalEntry, (MemTag)13>&, JavaThread*)+0x14b (aotStreamedHeapLoader.cpp:512)
V [libjvm.so+0x746984] AOTStreamedHeapLoader::TracingObjectLoader::materialize_root(int, Stack<AOTHeapTraversalEntry, (MemTag)13>&, JavaThread*)+0x44 (aotStreamedHeapLoader.cpp:524)
V [libjvm.so+0x74b33c] AOTStreamedHeapLoader::materialize_root(int)+0x46c (aotStreamedHeapLoader.cpp:1060)
V [libjvm.so+0x74b5ab] AOTStreamedHeapLoader::get_root(int)+0x11b (aotStreamedHeapLoader.cpp:1075)
V [libjvm.so+0x1076faf] HeapShared::get_root(int, bool)+0x16f (heapShared.cpp:628)
V [libjvm.so+0x107a35c] HeapShared::init_archived_fields_for(Klass*, ArchivedKlassSubGraphInfoRecord const*)+0x15c (heapShared.cpp:1768)
V [libjvm.so+0x107adce] HeapShared::initialize_from_archived_subgraph(JavaThread*, Klass*)+0x9e (heapShared.cpp:1652)
V [libjvm.so+0x1337524] JVM_InitializeFromArchive+0x2c4 (jvm.cpp:3365)
j jdk.internal.misc.CDS.initializeFromArchive(Ljava/lang/Class;)V+0 java.base@26-internal
j java.lang.reflect.Proxy$ProxyBuilder.<clinit>()V+82 java.base@26-internal