Recently I tried to build the ref guide only to find I didn't have the deps installed on that particular machine (mostly I do solr dev on my desktop cause it's faster). The error I got was unenlightening:
This happens because CheckLinksAndAnchors.main() is trying to list the files in the directory into which Jeckyll didn't put the html.... and getting null. I think the problem here is that we let the build continue when Jeckyll failed. Attaching patch to fail out when Jeckyll is not found with this message:
That at least will point the dev in the right direction, since clearly something required is not found.