google.protobuf.field_mask_pb2.FieldMask
The update mask applies to the resource. Only display_name,
description and parent_policy_tag can be updated and thus
can be listed in the mask. If update_mask is not provided,
all allowed fields (i.e. display_name, description and
parent) will be updated. For more information including the
FieldMask definition, see
https://developers.google.com/protocol-buffers/docs/reference/google.protobuf#fieldmask
If not set, defaults to all of the fields that are allowed
to update.