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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _filter_pb(field_or_unary):
 """Convert a specific protobuf filter to the generic filter type. Args: field_or_unary (Union[google.cloud.proto.firestore.v1beta1.\ query_pb2.StructuredQuery.FieldFilter, google.cloud.proto.\ firestore.v1beta1.query_pb2.StructuredQuery.FieldFilter]):
 A field or unary filter to convert to a generic filter. Returns: google.cloud.firestore_v1beta1.types.\ StructuredQuery.Filter: A "generic" filter. Raises: ValueError: If ``field_or_unary`` is not a field or unary filter. """

    if isinstance(field_or_unary, query_pb2.StructuredQuery.FieldFilter):
        return query_pb2.StructuredQuery.Filter(field_filter=field_or_unary)
    elif isinstance(field_or_unary, query_pb2.StructuredQuery.UnaryFilter):
        return query_pb2.StructuredQuery.Filter(unary_filter=field_or_unary)
    else:
        raise ValueError("Unexpected filter type", type(field_or_unary), field_or_unary)