Label with text value "0" parsed as null from XML object

[msalihaltun]

We use libsbgn.js to convert from XML object to sbgn object here. The XML file looks like the following before conversion (from Chrome console):

.

We convert the XML file to string and then use the libsbgnjs.Sbgn.fromXML() function to convert to sbgn object that has map.glyph.label fields as follows:

As can be seen, label "1" is parsed correctly but "0" is not.

Here is the original file used (converted to string and passed into the function):
test.xml.txt