message: handle val === null in getTypeNameFromField
diff: @@ -9,7 +9,7 @@ import {
  const getTypeNameFromField = (obj: object) =>
  Object.values(obj).reduce(
  (all, val) =>
  - typeof val !== 'object'
  + typeof val !== 'object' || val === null
  ? all
  : val.__typename !== undefined
  ? { ...all, [val.__typename]: true }
  