Register error handler
    Registers an exception handler on the app instance for every type of
    exception code werkzeug is aware about.

    :param app: flask.Flask - flask application instance
    :param handler: function - the handler
    :return: None

def register_error_handler(app, handler=None):
    """
    Register error handler
    Registers an exception handler on the app instance for every type of
    exception code werkzeug is aware about.

    :param app: flask.Flask - flask application instance
    :param handler: function - the handler
    :return: None
    """
    if not handler:
        handler = default_error_handler

    for code in exceptions.default_exceptions.keys():
        app.register_error_handler(code, handler)