In java.lang.classfile.CodeBuilder, there are a few inconsistencies in spec and implementation: exceptionCatch claims to accept null but doesn't; receiverSlot claims to throw IAE for instance methods; CodeAttribute.labelToBci claims to return -1 but throws IAE.

There's also some confusion around instruction-named factories: if_nonnull and if_null don't match ifnonnull and ifnull instruction mnemonic; some instructions aren't listed because they share factories or are deprecated.

We should clarify these problems in specification and update implementation/specification as fit.