Don't modify an object that is passed to components as props

React (and Relay) discourage you from modifying objects that are passed 
to components as props: 
https://reactjs.org/docs/components-and-props.html#props-are-read-only. 
The "data" passed to the Issueish constructor is sent directly from the 
props passed to IssueishListController, so we should treat them as 
immutable.

I thought that React froze objects passed as props in development mode 
to catch these issues. That's what's failing on CI - I have no idea why 
it isn't failing locally for us.

Author: smashwilson

lib/models/issueish.js

@@ -6,15 +6,13 @@ import {GHOST_USER} from '../helpers';
 
 export default class Issueish {
   constructor(data) {
-    if (data.author === null) {
-      data.author = GHOST_USER;
-    }
+    const author = data.author || GHOST_USER;
 
     this.number = data.number;
     this.title = data.title;
     this.url = new URL(data.url);
-    this.authorLogin = data.author.login;
-    this.authorAvatarURL = new URL(data.author.avatarUrl);
+    this.authorLogin = author.login;
+    this.authorAvatarURL = new URL(author.avatarUrl);
     this.createdAt = moment(data.createdAt, moment.ISO_8601);
     this.headRefName = data.headRefName;
     this.headRepositoryID = data.repository.id;