This seems to be an edge case for some video files.
When the metadata info 'tracks' XML element is empty, this code will blow up:
https://github.com/greatseth/mediainfo/blob/1eb021d8018a37b0cd3604d55c17a3e7a1eef56c/lib/mediainfo/tracks.rb#L40 since ::REXML::Element#text, i.e.: parameter.text will return nil.