title: Gatsby createTypes don't create localFile using File
body: <p>I have a problem to run Gatsby when there is a field in graphql that is empty (in cms sometimes the field will be empty sometimes not). I managed to solve this problem by adding in gatsby-node.js via createTypes the missing content. Unfortunately just as for the text using the string type works fine so for the photo using the File type subfield localFile is not created.  I need the localFile to appear even if there is no photo, the same way as photo is added. Does anyone have an idea how to solve this. Thanks a lot in advance for your help.</p>
  <p><em>gatsby-node.js</em></p>
  <pre><code>exports.sourceNodes = ({ actions }) =&gt; {
   const { createTypes } = actions
   const typeDefs = ` type StrapiPageEstimateRealizations implements Node { 
       Title: String
       Description: String
       Img: File
  } 
  
  ` 
  createTypes(typeDefs) 
  }
  </code></pre>
  <p><a href="https://i.stack.imgur.com/LMiLX.png" rel="nofollow noreferrer">graphql when the photo field is empty</a></p>
  <p><a href="https://i.stack.imgur.com/74aWd.png" rel="nofollow noreferrer">graphql when a picture is added in cms</a></p>