allow None as name in multi-index

Author: matiaslindgren

pandas/core/indexes/base.py

@@ -4516,8 +4516,8 @@ def _join_multi(self, other: Index, how: JoinHow):
         from pandas.core.reshape.merge import restore_dropped_levels_multijoin
 
         # figure out join names
-        self_names_list = list(com.not_none(*self.names))
-        other_names_list = list(com.not_none(*other.names))
+        self_names_list = list(self.names)
+        other_names_list = list(other.names)
         self_names_order = self_names_list.index
         other_names_order = other_names_list.index
         self_names = set(self_names_list)