blobstore/blobstore.go
func isErrFieldMismatch(err error) bool {
	_, ok := err.(*datastore.ErrFieldMismatch)
	return ok
}
func isErrFieldMismatch(err error) bool {
	_, ok := err.(*datastore.ErrFieldMismatch)
	return ok
}
// isErrFieldMismatch returns whether err is a datastore.ErrFieldMismatch.
//
// The blobstore stores blob metadata in the datastore. When loading that
// metadata, it may contain fields that we don't care about. datastore.Get will
// return datastore.ErrFieldMismatch in that case, so we ignore that specific
// error.