def __init__(self, failure=None, failures=None):
        """
        One of failure/failures must be set.
        
        :param failure: single (installer_key, message) tuple.  
        :param failures: list of (installer_key, message) tuples
        """
        if failures == None:
            self.failures = failures
        elif not failure:
            raise ValueError("failure is None")
        else:
            self.failures = [failure]
dataset/ETHPy150Open ros-infrastructure/rosdep/src/rosdep2/core.py/InstallFailed.__init__/operator `is not` -> `==`