code: @Override
      public void visitClassContext(ClassContext classContext) {
  
          try {
              if ((collectionClass == null) || (mapClass == null)) {
                  return;
              }
              stack = new OpcodeStack();
              fieldUserValues = new HashMap<>();
              classContext.getJavaClass().accept(this);
          } finally {
              fieldUserValues = null;
              stack = null;
          }
      }
docs: overrides the visitor to initialize the opcode stack
  
  @param classContext
  the currently parsed class