code: @Override
      public void visitTryCatchBlock(Label start, Label end, Label handler, String exceptionType) {
          if (enabled && exceptionType != null) {
              handlers.put(handler, Type.getObjectType(exceptionType));
          }
          super.visitTryCatchBlock(start, end, handler, exceptionType);
      }
docs: Callback used to determine the {@code Label}s that correspond to
  exception handlers.