title: Use @skip on "null" fields using graphql
body: <p>Given the following GQL</p>
  
  <pre><code>query getMembers {
    repository(owner: "nasa", name: "cumulus") {
      mentionableUsers(first: 100) {
        nodes {
          login
          organization(login: "nasa") {
            login
          }
        }
      }
    }
  }
  </code></pre>
  
  <p>(Query against GitHub v4 GraphQL)</p>
  
  <p>the value for <code>login</code> under <code>organization</code> is either <code>"nasa"</code> or <code>null</code></p>
  
  <p>I am trying to figure out if it's possible to use @skip against the login/organization so that only contributors to the repo, who are members of the nasa org are shown. I believe for this particular query you can do it another way, but this is just an example. </p>
  
  <p>How would you use @skip/@include with a non boolean. There is minimal documentation on this. While I could filter the response JSON in my client side app, it would be more efficient to receive less data sent over the network and then to parse in my app.</p>
  
  <p>Playing in GraphQLi I received errors trying this various ways - maybe its only possible if the field returns a boolean itself?</p>
  
  <p>e.g., I couldn't do <code>login @skip(if login==null)</code>. I also tried setting a value to null in the variables section and the referencing it in the query, but none of the variations I tried work.</p>
  
  <p>What I would really like to do is not include the parent if the child field is some value. e.g., if login=null then don't include that mentionable user. There is no search field option on mentionableUser. From my reading, I am guessing that the only way to do this would be if the API was modified to put a search or filter field on the mentionalbeUsers, otherwise I would need to do this with my client?</p>