Unhelpful error message on read of uninitialized field by crucible_jvm_verify

[brianhuffman]

When verifying a JVM method, it may happen that the symbolic tries to read an instance field or an array element, and fails because the value is uninitialized. (This may happen due to a missing points-to declaration in the method spec, for example.) But the error message when this happens is quite uninformative:

[20:19:53.913] Stack trace:
"crucible_jvm_verify" (/Users/huffman/Work/saw-script/intTests/test_jvm_method_names/test.saw:15:1-15:20):
Symbolic execution failed.
Abort due to false assumption:
  internal: error: in Test.get
  incorrect variant

It just says "incorrect variant", and doesn't give any clue about what caused the problem, what it was trying to do when it happened, or how to fix it.

In this case, the error occurred because it was trying to read the field called Test.val, of type long, but that field was uninitialized because I commented out the points-to precondition for that field in the SAW spec. The error message should at least include the name of the field it was trying to access.