gatsby-source-wordpress error: "An empty string was returned instead of a response when making a GraphQL request."

Question

Following the steps at the gatsby wordpress tutorial, I added the necessary plugins to my wordpress and created the gatsby code. Everything is properly fetched, except for posts, I receive the following error:

An empty string was returned instead of a response when making a GraphQL request. This may indicate that you have a WordPress filter running which is causing WPGraphQL to return an empty string instead of a response. Please open an issue with a reproduction at https://github.com/gatsbyjs/gatsby/issues/new for more help

Error occurred while updating a single "post" node.

ERROR

TypeError: Cannot read property 'post' of undefined at fetchAndCreateSingleNode (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/update-nodes/wp-actions/update.js:76:24) at processTicksAndRejections (internal/process/task_queues.js:95:5) at wpActionUPDATE (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/update-nodes/wp-actions/update.js:311:20) at handleWpActions (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/update-nodes/wp-actions/index.js:60:7) at fetchAndRunWpActions (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/update-nodes/wp-actions/index.js:102:7) at fetchAndApplyNodeUpdates (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/update-nodes/fetch-node-updates.js:44:36) at sourceNodes (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/steps/source-nodes/index.ts:60:5) at runSteps (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby-source-wordpress/src/utils/run-steps.ts:41:9) at runAPI (/Users/bbt/Documents/Work/my-wordpress-gatsby-site-2/node_modules/gatsby/src/utils/api-runner-node.js:462:16)

ERROR #gatsby-source-wordpress_112003

gatsby-source-wordpress

Encountered a critical error when running the sourceNodes.sourceNodes build step. See above for more information.

Relevant gatsby-config.js:

resolve: `gatsby-source-wordpress`,
       options: {
         url:
           process.env.WPGRAPHQL_URL ||
           `https://BLOGURL.com/graphql`,
         auth: {
           htaccess: {
             username: `HTACCESS-USERNAME`,
             password: `HTACCESS-PASSWORD`,
           },
         },
         schema: {
           perPage: 5, // making it slow (suggested somewhere)
           requestConcurrency: 5, // making it slow (suggested somewhere)
           previewRequestConcurrency: 2, // making it slow (suggested somewhere)
         },
       },

I can query the post nodes in the wordpress graphQL without a problem, they are there.

Any ideas how to debug this?

Answer 1

I solved it the following way -- switched off all plugins and it worked. Switched them back one-by-one, and there was a certain plugin (something related to external links, so absolutely not something that was suspicious) that caused the problem. It works since the plugin is switched off.