title: relay/ graphql: nullable response or a way to catch query error
body: <p>In relay/graphql, how to express a query where the response can be empty. I have a dilemma now that, I can't respond with an empty/null response because <code>id</code> field is required by relay (and possibly other non nullable fields in graphql schema), and I can't send error as it stops my component being rendered.</p>
  
  <p>For example, say I am modelling a relationship hierarchy and has a query like</p>
  
  <p><code>getSpouse(partnerID: string): Person</code></p>
  
  <p>and this may be empty for some. So, I do either respond with a null Person object (which I think is not quite possible with relay as Person might have non nullable fields including a globalID), or send an error. It is ok to send error, but I am not sure how to catch this error and continue with rendering relay container. I know hot to get errors in case of mutation but query is processed by relay container and couldn't see an interface to get error and continue loading the component.</p>
  
  <p>Is there a way to catch the query error at the Relay container or pass it down to my component ?</p>