CLN: Call to_frame and return None explicitly

- There is already a method which constructs a DataFrame from a Series:
  to_frame.
- There is no reason to check if result is None. In case result is None,
  simply return None explicitly.

Author: dahlbaek

pandas/core/series.py

@@ -2921,9 +2921,9 @@ def to_csv(self, path_or_buf=None, index=True, sep=",", na_rep='',
             Additional keyword arguments are passed to
             :func:`pandas.DataFrame.to_csv`
         """
-        from pandas.core.frame import DataFrame
-        df = DataFrame(self)
 
+        # convert to DataFrame
+        df = self.to_frame()
         # ensure backwards compatibility with path argument
         path_or_buf = kwargs.pop('path', path_or_buf)
         # result is only a string if no path_or_buf provided, otherwise None
@@ -2932,8 +2932,7 @@ def to_csv(self, path_or_buf=None, index=True, sep=",", na_rep='',
                            index_label=index_label, mode=mode,
                            encoding=encoding, compression=compression,
                            date_format=date_format, decimal=decimal, **kwargs)
-        if path is None:
-            return result
+        return result
 
     @Appender(generic._shared_docs['to_excel'] % _shared_doc_kwargs)
     def to_excel(self, excel_writer, sheet_name='Sheet1', na_rep='',