I keep getting this error for my me property in my React site. it is referencing this line of code

const PostForm = () => {
  const [postText, setText] = useState('');
  const [characterCount, setCharacterCount] = useState(0);

  const [addPost, { error }] = useMutation(ADD_POST, {
    update(cache, { data: { addPost } }) {
      try {
        // update post array's cache
        // could potentially not exist yet, so wrap in a try/catch
        const { posts } = cache.readQuery({ query: QUERY_POSTS });
        cache.writeQuery({
          query: QUERY_POSTS,
          data: { posts: [addPost, ...posts] },
        });
      } catch (e) {
        console.error(e);
      }

      // update me object's cache
      const { me } = cache.readQuery({ query: QUERY_ME });
      cache.writeQuery({
        query: QUERY_ME,
        data: { me: { ...me, posts: [...me.posts, addPost] } },
      });
    },
  });

  // update state based on form input changes
  const handleChange = (event) => {
    if (event.target.value.length <= 280) {
      setText(event.target.value);
      setCharacterCount(event.target.value.length);
    }
  };

  // submit form
  const handleFormSubmit = async (event) => {
    event.preventDefault();

    try {
      await addPost({
        variables: { postText },
      });

      // clear form value
      setText('');
      setCharacterCount(0);
    } catch (e) {
      console.error(e);
    }
  };

Does anyone have any idea where I should take a look at to troubleshoot this? Thank you so much!