code: def validate_context_for_visiting_vertex_field(parent_location, vertex_field_name, context):
      
      if is_in_fold_innermost_scope(context):
          raise GraphQLCompilationError(
              u'Traversing inside a @fold block after filtering on {} or outputting fields '
              u'is not supported! Parent location: {}, vertex field name: {}'
              .format(COUNT_META_FIELD_NAME, parent_location, vertex_field_name))
docs: Ensure that the current context allows for visiting a vertex field.