def nullable(property_schema):
 new_schema = property_schema.copy()
 new_schema['type'] = [property_schema['type'], 'null']
 return new_schema

def nullable ( property_schema ) : new_schema = property_schema . copy ( ) new_schema [ 'type' ] = [ property_schema [ 'type' ] , 'null' ] return new_schema
clone a property schema into one that is nullable .