'Checks if the cell at coordinates ``pt`` is either empty or
out of the bounds of the grid.'

@staticmethod
def _empty_point(pt, grid):

    if ((pt[0] < 0) or (pt[1] < 0) or (pt[0] >= grid.height) or (pt[1] >= grid.width)):
        return True
    return (grid[pt] is None)
