Fixed a bug with adjoint_times for spaces=None

src/operators/matrix_product_operator.py

@@ -132,7 +132,7 @@ class MatrixProductOperator(EndomorphicOperator):
                     mat_axes = np.flip(self._mat_last_n)
                     field_axes = self._mat_first_n
                     res = np.tensordot(m,x.val,axes=(mat_axes,field_axes))
-                    res = res.reshape(np.flip(res.shape))
+                    res = res.transpose()
             else:
                 res = m.dot(x.val.flatten()).reshape(self._domain.shape)
             return Field(self._domain, res)