BUG: handling of missing values in Index._reindex_non_unique with non unique target

Author: toobaz

pandas/core/indexes/base.py

@@ -3627,7 +3627,7 @@ def _reindex_non_unique(self, target):
             else:
 
                 # need to retake to have the same size as the indexer
-                indexer[~check] = 0
+                indexer[~check] = -1
 
                 # reset the new indexer to account for the new size
                 new_indexer = np.arange(len(self.take(indexer)))