title: How to filter GraphQL results by a descendent without edges?
body: <p>I just started looking at GraphQL and I am wondering if there is a way to filter results that don't have any nodes. Here is a relatively simple example query:</p>
  
  <pre><code>query { 
    organization(login:"GitHub") { 
      repositories(first: 20) {
        edges {
          node {
            name
            pullRequests(first: 5, states: OPEN){
              edges {
                node {
                  title
                  author{
                    login
                  }
                  updatedAt
                }
              }
            }
          }
        }
      }
    }
  }
  </code></pre>
  
  <p>and here is a subset of the results that query returns:</p>
  
  <pre><code>{
    "data": {
      "organization": {
        "repositories": {
          "edges": [
            {
              "node": {
                "name": "gitignore",
                "pullRequests": {
                  "edges": [
                    {
                      "node": {
                        "title": "Create new CodeComposerStudio.gitignore",
                        "author": {
                          "login": "wolf99"
                        },
                        "updatedAt": "2017-07-26T20:31:53Z"
                      }
                    },
                    {
                      "node": {
                        "title": "Create PVS.gitignore",
                        "author": {
                          "login": "cesaramh"
                        },
                        "updatedAt": "2017-05-01T19:42:07Z"
                      }
                    },
                    {
                      "node": {
                        "title": "gitignore for Magic Software Enterprises product xpa ",
                        "author": {
                          "login": "tommes"
                        },
                        "updatedAt": "2017-05-01T19:41:53Z"
                      }
                    },
                    {
                      "node": {
                        "title": "Create PSoC.gitignore",
                        "author": {
                          "login": "dbrwn"
                        },
                        "updatedAt": "2017-05-01T19:41:39Z"
                      }
                    },
                    {
                      "node": {
                        "title": "add ThinkPHP gitignore file",
                        "author": {
                          "login": "swumao"
                        },
                        "updatedAt": "2017-05-01T19:40:53Z"
                      }
                    }
                  ]
                }
              }
            },
            {
              "node": {
                "name": "dmca",
                "pullRequests": {
                  "edges": []
                }
              }
            }
          ]
        }
      }
    }
  }
  </code></pre>
  
  <p>So I'd like to know if there is a way to modify my query so that it would not return the node named <code>dmca</code> since there are no edges on <code>pullRequests</code>.</p>