def changed(requestContext, seriesList):
    """
    Takes one metric or a wildcard seriesList.
    Output 1 when the value changed, 0 when null or the same
    Example::

        &target=changed(Server01.connections.handled)
    """
    for series in seriesList:
        series.name = series.pathExpression = 'changed(%s)' % series.name
        previous = None
        for index, value in enumerate(series):
            if previous is None:
                series[index] = 0
            elif value is not None and previous != value:
                series[index] = 1
            else:
                series[index] = 0
            previous = value
    return seriesList
