code: @Override
      public void visitClassContext(ClassContext classContext) {
          try {
              unusedParms = new BitSet();
              regToParm = new HashMap<>();
              stack = new OpcodeStack();
              super.visitClassContext(classContext);
          } finally {
              stack = null;
              regToParm = null;
              unusedParms.clear();
          }
      }
docs: implements the visitor to create parm bitset
  
  @param classContext
  the context object of the currently parsed class