pydata/pandas — pull request #3701 by tdsmith (2013-05-28 05:14:38+00:00)
Title: BUG: DataFrame.to_csv fails silently if nanRep not None

The nanRep argument to DataFrame.to_csv() is deprecated and na_rep should be used instead. .to_csv should succeed with a warning if nanRep is specified. Before this fix, to_csv threw a warning but did not save the file.