avoid infinite recursion

Author: minggli

pandas/core/internals/blocks.py

@@ -999,8 +999,8 @@ def putmask(self, mask, new, align=True, inplace=False, axis=0,
                 if not (mask.shape[-1] == len(new) or
                         mask[mask].shape[-1] == len(new) or
                         len(new) == 1):
-                    raise ValueError("cannot assign mismatch "
-                                     "length to masked array")
+                    raise NotImplementedError("cannot assign mismatch "
+                                              "length to masked array")
 
             np.putmask(new_values, mask, new)