TypeError when trying to convert several SLDs

[sbsimo]

Hello, I tried to run the script for working on several SLDs, but always get the same error (below).
I'm working with node v8.10.0 and Ubuntu 18.04.4 LTS.
Can it be due to the namespace (sld:) in front of the tags in my input SLDs?
Or the issue is related to compatibility with the dependency versions?
Thanks a lot!

sample of SLD input:
<?xml version="1.0" encoding="ISO-8859-1" standalone="yes"?> <sld:StyledLayerDescriptor version="1.0.0" xmlns:sld="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xlink="http://www.w3.org/1999/xlink"> <sld:NamedLayer>...

events.js:183
throw er; // Unhandled 'error' event
^

TypeError: Cannot read property 'NamedLayer' of undefined
at /root/viewer/SLDexit/SLD_to_JSON.js:239:57
at Parser. (/root/viewer/SLDexit/node_modules/xml2js/lib/parser.js:304:18)
at emitOne (events.js:116:13)
at Parser.emit (events.js:211:7)
at SAXParser.onclosetag (/root/viewer/SLDexit/node_modules/xml2js/lib/parser.js:262:26)
at emit (/root/viewer/SLDexit/node_modules/sax/lib/sax.js:624:35)
at emitNode (/root/viewer/SLDexit/node_modules/sax/lib/sax.js:629:5)
at closeTag (/root/viewer/SLDexit/node_modules/sax/lib/sax.js:889:7)
at SAXParser.write (/root/viewer/SLDexit/node_modules/sax/lib/sax.js:1436:13)
at Parser.exports.Parser.Parser.parseString (/root/viewer/SLDexit/node_modules/xml2js/lib/parser.js:323:31)