This is a minimal reproduction of an issue that I'm seeing with Gatsby's graphql API.

To reproduce the problem:

1. Clone this repository.
2. Run yarn install to install dependencies.
3. Run yarn start to start the server.
4. When the server comes up, open http://localhost:8000/___graphql in a web browser.
5. In GraphIQL, run this query:

   query MyQuery {
     markdownRemark(frontmatter: {path: {eq: "/mypage.html"}}) {
       frontmatter {
         path
         title
       }
     }
     topicInternalHeadings(path: {eq: "/mypage.html"}) {
       headings {
         level
         path
         text
       }
     }
   }

6. Note that the query returns data for the topicInternalHeadings node.
7. Go to http://localhost:8000/myPage.html.
8. In the console, note that the data returned from the page query includes no data for the topicInternalHeadings node:

   {markdownRemark: {…}, topicInternalHeadings: null}
   

Expected result: Node data appears in the log and on the page because the data is visible in graphiql.

The code in plugins/gatsby-remark-internal-toc/index.js creates the topicInternalHeadings nodes.