Change head.repo on pull requests to Option

[ashawley]

Pull requests can have their forks deleted:

• https://stackoverflow.com/questions/36071272/fix-unknown-repository-of-an-opened-pr-after-deleted-the-fork
• Pull request displays "unknown repo" after deletion of fork isaacs/github#168

This means the head.repo could be null, although this isn't documented in the API doc for listing pull requests:

https://developer.github.com/v3/pulls/#list-pull-requests

This causes github-api to throw an exception:

java.util.NoSuchElementException: None.get

Here's how to recreate the bug with a JSON payload in a file.

import org.json4s.JArray
import org.json4s.jackson.JsonMethods.parse
import codecheck.github.models.PullRequest

val json = scala.io.Source.fromFile("data/prs.json").getLines.mkString
parse(json).asInstanceOf[JArray].arr.map(PullRequest(_)).map(_.head.repo.name)

[ashawley]

Here is an example of a null repo:

[
  {
    "url": "https://api.github.com/repos/octocat/Hello-World/pulls/1347",
    "id": 1,
    ...
    "head": {
      "label": "new-topic",
      "ref": "new-topic",
      "sha": "e245d1f90f74d67be6635121572c7f83d130c822",
      "user": {
        "login": "octocat",
	...
      },
      "repo": null
    },
    "base": {
      "label": "master",
      "ref": "master",
      "sha": "6dcb09b5b57875f334f61aebed695e2e4193db5e",
      "user": {
        "login": "octocat",
	...
      },
      "repo": {
        "id": 1296269,
        "owner": {
          "login": "octocat",
	  ...
	},
      }
    }
    ...
  },
  ...
]