to_csv - parameter decimal
I think that pandas.to_csv does not properly process the decimal parameter. It seems it is ignored whenever the dataframe to be exported contains a NaN value. This means it is not possible to export pandas in European CSV format.

I am aware that problems with to_csv have been discussed earlier and from these discussions I found the hint to check for NaN values. I am afraid I do not understand the final outcome of alle these previous discussions but I think the current behaviour is not quite correct. 

