def get_default_values(json_data):
    """
    Method to make default values dict for properties in json schema.
    Set default value as None if property havent 'default' key in schema

    :param json_data: json schema with properties as dict with 'default'
                    keys or without it
    :return: dict with default values for all properties in given schema
    """

    default_properties_values = dict()
    # make defaults for all properties
    for property_name in json_data['properties']:
        # if schema have 'default' value for property
        if 'default' in json_data['properties'][property_name].keys():
            default_value = json_data['properties'][property_name]['default']
        # use None as default default value
        else:
            default_value = None

        default_properties_values[property_name] = default_value

    return default_properties_values