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ACF Relationship Field throws an error in Gatsby

See original GitHub issue

I’m running into a problem, where a query throws an error, which works on the remote GraphiQL endpoint, when using an ACF Relationship field.

query {
  page(id: "730", idType: DATABASE_ID) {
    acf {
      content {
        ... on Page_Acf_Content_FeaturedNews {
          news {
            ... on NewsEntry {
              id
            }
          }
        }
      }
    }
  }
}

returns on the remote GraphiQL:

{
  "data": {
    "page": {
      "acf": {
        "content": [
          {
            "news": [
              {
                "id": "cG9zdDoyNjI4"
              },
              {
                "id": "cG9zdDoyNjMy"
              },
              {
                "id": "cG9zdDoyNjE3"
              }
            ]
          }
        ]
      }
    }
  }
}

but the same query throws an error in Gatsby:

query MyQuery {
  wpPage(databaseId: {eq: 730}) {
    acf {
      content {
        ... on WpPage_Acf_Content_FeaturedNews {
          news {
            ... on WpNewsEntry {
              id
            }
          }
        }
      }
    }
  }
}

result:

{
  "errors": [
    {
      "message": "Cannot read property 'id' of null",
      "locations": [
        {
          "line": 6,
          "column": 11
        }
      ],
      "path": [
        "wpPage",
        "acf",
        "content",
        5,
        "news"
      ],
      "stack": [
        "TypeError: Cannot read property 'id' of null",
        "    at reduce (~/node_modules/gatsby-source-wordpress-experimental/src/steps/create-schema-customization/transform-fields/transform-union.js:49:27)",
        "    at Array.reduce (<anonymous>)",
        "    at resolver (~/node_modules/gatsby-source-wordpress-experimental/src/steps/create-schema-customization/transform-fields/transform-union.js:46:28)",
        "    at wrappedTracingResolver (~/node_modules/gatsby/src/schema/resolvers.ts:518:14)",
        "    at resolveFieldValueOrError (~/node_modules/graphql/execution/execute.js:467:18)",
        "    at resolveField (~/node_modules/graphql/execution/execute.js:434:16)",
        "    at executeFields (~/node_modules/graphql/execution/execute.js:275:18)",
        "    at collectAndExecuteSubfields (~/node_modules/graphql/execution/execute.js:713:10)",
        "    at completeObjectValue (~/node_modules/graphql/execution/execute.js:703:10)",
        "    at completeAbstractValue (~/node_modules/graphql/execution/execute.js:660:10)",
        "    at completeValue (~/node_modules/graphql/execution/execute.js:585:12)",
        "    at completeValueCatchingError (~/node_modules/graphql/execution/execute.js:495:19)",
        "    at ~/node_modules/graphql/execution/execute.js:618:25",
        "    at Array.forEach (<anonymous>)",
        "    at forEach (~/node_modules/iterall/index.js:83:25)",
        "    at completeListValue (~/node_modules/graphql/execution/execute.js:614:24)",
        "    at completeValue (~/node_modules/graphql/execution/execute.js:573:12)",
        "    at ~/node_modules/graphql/execution/execute.js:492:16",
        "    at runMicrotasks (<anonymous>)",
        "    at processTicksAndRejections (internal/process/task_queues.js:93:5)",
        "    at async Promise.all (index 0)",
        "    at async Promise.all (index 0)",
        "    at async Promise.all (index 0)"
      ]
    }
  ],
  "data": {
    "wpPage": {
      "acf": {
        "content": [
          {
            "news": null
          }
        ]
      }
    }
  }
}

kolle-on-xps :: Development/ » npx gatsby info

System: OS: Linux 5.8 Ubuntu 20.10 (Groovy Gorilla) CPU: (8) x64 Intel® Core™ i7-10510U CPU @ 1.80GHz Shell: 5.8 - /usr/bin/zsh Binaries: Node: 14.15.1 - /usr/bin/node Yarn: 1.22.4 - ~/.npm-global/bin/yarn npm: 6.14.8 - ~/.npm-global/bin/npm Languages: Python: 2.7.18 - /usr/bin/python Browsers: Firefox: 83.0 npmPackages: gatsby: ^2.24.91 => 2.27.0 gatsby-image: ^2.6.0 => 2.6.0 gatsby-link: ^2.4.16 => 2.6.0 gatsby-plugin-advanced-sitemap: ^1.5.6 => 1.5.6 gatsby-plugin-manifest: ^2.4.37 => 2.7.0 gatsby-plugin-netlify: ^2.3.25 => 2.6.0 gatsby-plugin-react-helmet: ^3.3.14 => 3.5.0 gatsby-plugin-react-svg: ^3.0.0 => 3.0.0 gatsby-plugin-sharp: ^2.6.43 => 2.9.0 gatsby-plugin-styled-jsx: ^3.5.0 => 3.5.0 gatsby-source-filesystem: ^2.3.37 => 2.6.1 gatsby-source-wordpress-experimental: ^3.1.3 => 3.1.3 gatsby-transformer-sharp: ^2.5.20 => 2.7.0

using WPGraphQL: 1.0