nullable-milestone

record nullable-milestone {
  closed-at: string,
  closed-issues: s32,
  created-at: string,
  creator: nullable-simple-user,
  description: string,
  due-on: string,
  html-url: string,
  id: s32,
  labels-url: string,
  node-id: string,
  number: s32,
  open-issues: s32,
  state: nullable-milestone-state-enum,
  title: string,
  updated-at: string,
  url: string,
}