title: Nest JS GraphQL “Cannot return null for non-nullable”
body: <p>I tried to resolve one error in my study code, but failed. Then I just try to launch this code...</p>
  
  <p><a href="https://github.com/nestjs/nest/tree/master/sample/23-type-graphql" rel="noreferrer">https://github.com/nestjs/nest/tree/master/sample/23-type-graphql</a></p>
  
  <p>and the same situation...</p>
  
  <p>Error looks like</p>
  
  <pre><code>{
    "errors": [
      {
        "message": "Cannot return null for non-nullable field Recipe.id.",
        "locations": [
          {
            "line": 3,
            "column": 5
          }
        ],
        "path": [
          "recipe",
          "id"
        ],
        "extensions": {
          "code": "INTERNAL_SERVER_ERROR",
          "exception": {
            "stacktrace": [
              "Error: Cannot return null for non-nullable field Recipe.id.",
              "    at completeValue (/home/innistry/Downloads/nest-master/sample/23-type-graphql/node_modules/graphql/execution/execute.js:560:13)",
              "    at /home/innistry/Downloads/nest-master/sample/23-type-graphql/node_modules/graphql/execution/execute.js:492:16",
              "    at process._tickCallback (internal/process/next_tick.js:68:7)"
            ]
          }
        }
      }
    ],
    "data": null
  }
  </code></pre>
  
  <p>Has someone ideas?</p>