def shrink_mask(self):
m = self._mask<EOL>if m.ndim and not m.any():<EOL><INDENT>self._mask = nomask<EOL><DEDENT>return self<EOL>
Reduce a mask to nomask when possible.

Parameters
----------
None

Returns
-------
None

Examples
--------
>>> x = np.ma.array([[1,2 ], [3, 4]], mask=[0]*4)
>>> x.mask
array([[False, False],
       [False, False]], dtype=bool)
>>> x.shrink_mask()
>>> x.mask
False