code: public MethodNode addMethod(String name,
                                  int modifiers,
                                  ClassNode returnType,
                                  Parameter[] parameters,
                                  ClassNode[] exceptions,
                                  Statement code) {
          MethodNode other = getDeclaredMethod(name, parameters);
          // let's not add duplicate methods
          if (other != null) {
              return other;
          }
          MethodNode node = new MethodNode(name, modifiers, returnType, parameters, exceptions, code);
          addMethod(node);
          return node;
      }
docs: If a method with the given name and parameters is already defined then it is returned
  otherwise the given method is added to this node. This method is useful for
  default method adding like getProperty() or invokeMethod() where there may already
  be a method defined in a class and so the default implementations should not be added
  if already present.