What is it

Do not prematurely return, throw an explicit error such as 404

• Prematurely returning a data will result in type drift instead (since it is a partial result)

Non-null argument in querying

The Non-Null type modifier (!) can also be used when defining arguments for a field, which will cause the GraphQL server to return a validation error if a null value is passed as that argument, whether in the GraphQL string or in the variables.

# query definition in front end
query DroidById($id: ID!) {
  droid(id: $id) {
    name
  }
}

# client query param
{
  "id": null
}

# returned result from GQL server
{
  "errors": [
    {
      "message": "Variable \"$id\" of non-null type \"ID!\" must not be null.",
      "locations": [
        {
          "line": 1,
          "column": 17
        }
      ]
    }
  ]
}