Non-verbose crash on input containing NaN

[LucaCappelletti94]

Hello and thank you for creating this library!

Some students of mine got stuck trying to use this library when they where providing wrongfully data forgetting to impute the NaN values and the library would just crash without any message specifying the nature of the error.

I will be making a pull request shortly to address this case and to add an exception that explains what needs to be fixed.