I am reading a paper, let $h:Z\rightarrow Y$ be a bimeromorphic morphism between normal complex varieties, so h is an isomorphic over an analytic Zariski open subset of codimension $\ge 2$ in $Y$, the author then claims that: for every Weil divisor $D$ on $Z$,
$$h_*\mathcal O_Z(D) \quad\text{and}\quad\mathcal O_Y(h_*D) \quad\text{are isomorphic in codimension 1.}$$
Here, $h_*D$ denotes the direct image of $D$, and $h_*\mathcal O_Z(D)$ denotes the direct image sheaf, I can't figure out why they are isomorphic in codimension 1 rather than codimension 2. In fact, I have no idea to prove it strictly...
Any help would be appreciated. Thanks in advance!