bug(NDFrame): indexer for MultiIndex only if level is provided.

Author: wojtek2kdev

pandas/core/generic.py

@@ -1147,11 +1147,11 @@ def rename(
 
             # GH 13473
             if not callable(replacements):
-                if ax._is_multi:
+                if ax._is_multi and level is not None:
                     indexer = ax.get_level_values(level).get_indexer_for(replacements)
                 else:
                     indexer = ax.get_indexer_for(replacements)
-                
+
                 if errors == "raise" and len(indexer[indexer == -1]):
                     missing_labels = [
                         label