'Check whether all grid lines are in the same visibility state.
Returns True/False if all grid lines are on or off, None if they are
not all in the same state.'

@staticmethod
def _get_uniform_grid_state(ticks):

    if all((tick.gridOn for tick in ticks)):
        return True
    elif (not any((tick.gridOn for tick in ticks))):
        return False
    else:
        return None
