Repro:
- clone repo
- run "yarn install"
- run "yarn start"
- open "http://localhost:3998/" in browser
- run mutation: " mutation { createUser(name: "some name") { id name } } "
- observe that it runs correctly
- open "http://localhost:3999/" in browser
- run same mutation: " mutation { createUser(name: "some name") { id name } } "
- observe error: "Cannot return null for non-nullable field Mutation.createUser."
- if you move line #13 "createUser(name: String!): User!" up to #7 inside Mutation in userServerSchemaString.js file, everything will work.