Address NullPointerException if the users has not specified a baseline hash for directory

[dennis-behm]

This addresses defect #674 when multiple directories are on applicationSrcDirs, but the user does not have specified a baseline ash for each directory, like outlined in docs/BUILD.md

[wfezzani]

I suggest the following change which has been tested and validated:

String baselineRef = props.baselineRef ? buildUtils.getUserProvidedBaselineRef(dir) : null
String userBaselineRef = baselineRef ? userBaselineRef.replaceAll("origin/","")