Sorry not following the issue reporting instruction but this one is a simple error happening here
If the backend response payload=null (I know it shouldn't) and because Javascript consider the "null" as an object it throws error when trying resolve "payload.errors"
Indeed it passes through the guard that I think it's provided to prevent this kind of errors.

    if (this.isSuccess(status, headers, payload)) {
      return payload;
    } else if (this.isInvalid(status, headers, payload)) {
      return new InvalidError(typeof payload === 'object' && 'errors' in payload ? payload.errors : undefined);
    }