code: @Nonnull
    public ApiFuture<WriteResult> delete(@Nonnull Precondition options) {
      WriteBatch writeBatch = firestore.batch();
      return extractFirst(writeBatch.delete(this, options).commit());
    }
docs: Deletes the document referred to by this DocumentReference.
  
  @param options Preconditions to enforce for this delete.
  @return An ApiFuture that will be resolved when the delete completes.