code: @Override
      public void visitClassContext(ClassContext classContext) {
          try {
              stack = new OpcodeStack();
              storeToUserValue = new HashMap<>();
              allocLocation = new HashMap<>();
              allocToAddPCs = new HashMap<>();
              optionalRanges = new ArrayList<>();
              super.visitClassContext(classContext);
          } finally {
              stack = null;
              storeToUserValue = null;
              allocLocation = null;
              allocToAddPCs = null;
              optionalRanges = null;
          }
      }
docs: overrides the visitor to initialize the opcode stack
  
  @param classContext
  the context object that holds the JavaClass being parsed