This stack overflow seems to be occurring in the ‘shurcooL’ package itself: graphql/query.go at 3cf50f8a0a295163db1d360b4de28fb3cb874913 · shurcooL/graphql · GitHub
I’m not familiar with the ‘shurcooL’ package myself. Have you tried that mutation with Postman or Insomnia or other GraphQL clients?