"non-arpeggiate" creates invalid XML export

When exporting a Music XML whenever there is a non-arpeggiate in the score it creates invalid data into the XML file.

I've managed to isolated the bug. I'm attaching the .mscz and it's .musicxml.

In the musicxml you can see line 121.

< default-x="-14.80" default-y="15.51"/>

It occurs because of the "non-arpeggiate" in Line 136.

<non-arpeggiate type="top" default-x="-14.80" default-y="15.51"/>

You can add more "non-arpegiate"s and you'll see that for each one there will be a line like that with mal-formed XML. The "default-x" value will be the same in the non-arpeggiate and the problematic line.