docs: public boolean isNullCheck() {
          // Null check blocks must be exception throwers,
          // and are always empty. (The only kind of non-empty
          // exception throwing block is one terminated by an ATHROW).
          if (!isExceptionThrower() || getFirstInstruction() != null) {
              return false;
          }
          short opcode = exceptionThrower.getInstruction().getOpcode();
          return nullCheckInstructionSet.get(opcode);
      }