title: How to return both error and data in a graphql resolver?
body: <p>I was thinking about ways of implementing graphql response that would contain both an error and data.</p>
  
  <p>Is it possible to do so without creating a type that would contain <code>error</code>?</p>
  
  <p>e.g.</p>
  
  <p>Mutation <code>addMembersToTeam(membersIds: [ID!]! teamId: ID!): [Member]</code> adds members to some team. Suppose this mutation is called with the following <code>membersIds</code>: <code>[1, 2, 3]</code>.</p>
  
  <p>Members with ids 1 and 2 are already in the team, so an error must be thrown that these members cannot be added, but member with an id 3 should be added as he is not in the team. </p>
  
  <p>I was thinking about using <code>formatResponse</code> but seems that I can't get an error there.</p>
  
  <p>Is it possible to solve this problem without adding error field to the return type?</p>