Fix registerNodeClass with abstract class crashing

This always results in a segfault when trying to instantiate, so this never
worked. At least throw an error instead of segfaulting to p

Fix registerNodeClass with abstract class crashing

This always results in a segfault when trying to instantiate, so this never
worked. At least throw an error instead of segfaulting to prevent developers
from being confused.

Closes GH-12420.

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