use rs[mask] instead of rs.mask(mask,...

Author: sdementen

pandas/core/generic.py

@@ -5784,7 +5784,7 @@ def pct_change(self, periods=1, fill_method='pad', limit=None, freq=None,
                                   **kwargs)) - 1)
         if freq is None:
             mask = isnull(_values_from_object(self))
-            rs.mask(mask, np.nan, inplace=True)
+            rs[mask] = np.nan
         return rs
 
     def _agg_by_level(self, name, axis=0, level=0, skipna=True, **kwargs):