'Returns True if ``self`` is a zero module.
(If, as this implementation assumes, the coefficient ring is not the
zero ring, then this is equivalent to the rank being zero.)
>>> from sympy.abc import x
>>> from sympy import QQ
>>> QQ.old_poly_ring(x).free_module(0).is_zero()
True
>>> QQ.old_poly_ring(x).free_module(1).is_zero()
False'

def is_zero(self):

    return (self.rank == 0)
