onPostBuild graphql query returns empty object

[dwainetrain]

I'm trying to build a json file after the site builds, but my graphql query is returning an empty object. Here's the code from the gatsby-node.js

exports.onPostBuild = async ({ graphql }) => {
  await graphql(`
    query inventoryQuery {
      artworkInventory: allContentfulArtwork {
        nodes {
          id
          title
          price
          slug
        }
      }
    }
  `).then((result) => {
    console.log("Query result: ", result);
    const inventoryPath = "./artworks/";
    const artworks = result.data.artworkInventory.nodes.map(({ node }) => node);

    if (!fs.existsSync(inventoryPath)) fs.mkdirSync(inventoryPath);

    artworks.map((artwork) => {
      const data = { ...artwork, slug: artwork.slug };
      fs.writeFileSync(
        `${inventoryPath}/${data.slug}.json`,
        JSON.stringify(data)
      );
    });
  });
};

And I get this result (and other obvious errors because the data isn't there):

Query result:  {
  data: [Object: null prototype] {
    artworkInventory: [Object: null prototype] { nodes: [Array] }
  }
}

Any ideas on why the query isn't working? It works when building pages.