public static UnionTypeDefinitionNode Rename(
     this UnionTypeDefinitionNode unionTypeDefinition,
     NameString newName,
     IEnumerable <NameString> schemaNames)
 {
     return(AddSource(unionTypeDefinition, newName, schemaNames,
                      (n, d) => unionTypeDefinition
                      .WithName(n).WithDirectives(d)));
 }