In product builds, ArchiveHeapTestClass is a constant, hard coded to null.

It's used in unreachable code in product builds:

https://github.com/openjdk/jdk/blob/e73796879299c6170b63edb998439db4764ceae0/src/hotspot/share/cds/heapShared.cpp#L1428-L1437

#ifndef PRODUCT
   ...
#else
    bool is_test_class = false;
#endif

    if (is_test_class) {
      log_warning(cds)("Loading ArchiveHeapTestClass %s ...", ArchiveHeapTestClass);
    }

Nevertheless, sometimes gcc will warn that ArchiveHeapTestClass is a null pointer.