DEPR: True for dropna of SeriesGroupBy.nth (pandas-dev#11038)

Author: tnir

pandas/core/groupby.py

@@ -55,7 +55,7 @@
                                  compress_group_index, get_flattened_iterator,
                                  decons_obs_group_ids, get_indexer_dict)
 from pandas.util._decorators import (cache_readonly, Substitution,
-                                     Appender, make_signature)
+                                     Appender, make_signature, deprecate_kwarg)
 from pandas.io.formats.printing import pprint_thing
 from pandas.util._validators import validate_kwargs
 
@@ -3329,6 +3329,11 @@ def _apply_to_column_groupbys(self, func):
         """ return a pass thru """
         return func(self)
 
+    @deprecate_kwarg(old_arg_name='dropna', new_arg_name='dropna',
+                     mapping={True: None})
+    def groupby(self, by, **kwds):
+        return super(self, by)
+
 
 class NDFrameGroupBy(GroupBy):