Programmatically create pages from data fails

[billp72]

I'm trying to createpages. It works when I use gatsby develop but it fails when I use gatsby build

const Project = ({ data }) => {
  34 |   const post = data.markdownRemark;
> 35 |   const featuredImgFluid = post.frontmatter.featuredImage.childImageSharp.fluid;
     |                                                           ^
  36 |   return (
  37 |     <Layout>
  38 |       <Container>


  WebpackError: TypeError: Cannot read property 'childImageSharp' of null

  - project.js:35 Project
    src/templates/project.js:35:59

  - gatsby-ssr.js:14 Module.replaceRenderer
    gatsby-ssr.js:14:40

exports.onCreateNode = ({ node, getNode, actions }) => {
  const { createNodeField } = actions;
  if (node.internal.type === 'MarkdownRemark') {
    const slug = createFilePath({ node, getNode, basePath: 'content' });
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    });
  }
};

exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions;
  const result = await graphql(`
    query {
      allMarkdownRemark {
        edges {
          node {
            fields {
              slug
            }
          }
        }
      }
    }
  `);
  result.data.allMarkdownRemark.edges.forEach(({ node }) => {
      createPage({
        path: node.fields.slug,
        component: path.resolve(`./src/templates/project.js`),
        context: {
          // Data passed to context is available
          // in page queries as GraphQL variables.
          slug: node.fields.slug,
        },
      });
  });
};