How to get an issue associated to a pull request

I was trying to execute:

{
  repository(owner: "repo", name: "name") {
    pullRequest: issueOrPullRequest(number: 1) {
      __typename
      ... on PullRequest {
        timelineItems(itemTypes:CROSS_REFERENCED_EVENT) {
          ... on PullRequestTimelineItemsConnection {
            edges {
              node {
                ... on CrossReferencedEvent {
                  source {
                    ... on Issue {
                      title
                      number
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

But got the following error 

{
  "errors": [
    {
      "message": "Something went wrong while executing your query. Please include `B90D:3C5F0:2454CA5:299FAC0:5EC1ACDD` when reporting this issue."
    }
  ]
}

I am trying to get the issue associated to the pull request or more specifically the issue that is being fixed by this pull request.