Write Excel fails with non-descript error.

Hi,

Just testing out your Excel writer.

Found out that it doesn't handle nulls.  Would it be possible for the writer to simply create an empty cell here?  Took me a couple seconds to make sure nulls were causing the whole writer to fail.  I'm not sure if this is common practice but in large arrays, I use nulls as place spacers for rotation of an array of data.

Haven't tried the other tools but I surely appreciate you sharing this tool kit with us!