Merge intervals in the form of a list.

def merge_intervals(intervals):
    """ Merge intervals in the form of a list. """
    if intervals is None:
        return None
    intervals.sort(key=lambda i: i[0])
    out = [intervals.pop(0)]
    for i in intervals:
        if out[-1][-1] >= i[0]:
            out[-1][-1] = max(out[-1][-1], i[-1])
        else:
            out.append(i)
    return out