LPS-50700 force a NPE when source or target are null

When null is given as an argument to InputSource constructor, it fails
with a java.net.MalformedURLException, which is confusing (and doesn't
make any sense in our case).

Fail with NPE to make the API a little saner.
LPS-50700 unit tests for DiffHtml
LPS-50700 Use the right import
LPS-50700 Rename
LPS-50700 auto SF
LPS-50813 removed legacy clause
LPS-50778 - Move temp files to target run-selenium-tcat in build-test-tcat.xml
LPS-50821 Sync connector is not receiving updates when checked out files are restored from trash
LPS-50827 Make ConvertProcesses contributable through OSGi modules instead of portal.properties
LPS-50827 Publish ConvertProcesses to OSGi registry by making them Spring beans
LPS-50827 We don't need to explicitly implement the interface
LPS-50827 If we remove it, we need to remove it from the DTD and also warn ppl if they set it in portal-ext.properties