Fix

I was using https://github.com/rsdoiel/extractor-js and was getting this error:

/Users/mcollins/projects/wolf/node_modules/extractor/node_modules/jsdom/node_modules/nwmatcher/src/nwmatcher-noqsa.js:233
  contains = 'compareDocumentPosition' in root ?
                                          ^
TypeError: Cannot use 'in' operator to search for 'compareDocumentPosition' in null
    at /Users/mcollins/projects/wolf/node_modules/extractor/node_modules/jsdom/node_modules/nwmatcher/src/nwmatcher-noqsa.js:233:43

Found that root was not always defined in nwatcher so put in a fix to stop this. Worked for my usage, not sure if there is a more elegant fix you would like to try!