code: @Override
      public void visitClassContext(ClassContext classContext) {
          try {
              if ((throwableClass != null) && !isPre14Class(classContext.getJavaClass())) {
                  stack = new OpcodeStack();
                  catchInfos = new HashSet<>();
                  exReg = new HashMap<>();
                  super.visitClassContext(classContext);
              }
          } finally {
              stack = null;
              catchInfos = null;
              exceptions = null;
              exReg = null;
          }
      }
docs: implements the visitor to make sure the jdk is 1.4 or better
  
  @param classContext
  the context object of the currently parsed class