code: def _normalize_projection(projection):
          
          if projection is not None:
  
              fields = list(projection.fields)
  
              if not fields:
                  field_ref = query_pb2.StructuredQuery.FieldReference(
                      field_path="__name__"
                  )
                  return query_pb2.StructuredQuery.Projection(fields=[field_ref])
  
          return projection
docs: Helper:  convert field paths to message.