* Remove a source-target/variant from the specDAG.
*/
private void removeSTV(final String source, final String target, final String variant) {
// assert(source.length() > 0);
// assert(target.length() > 0);
CaseInsensitiveString cisrc = new CaseInsensitiveString(source);
CaseInsensitiveString citrg = new CaseInsensitiveString(target);
CaseInsensitiveString civar = new CaseInsensitiveString(variant);
Map<CaseInsensitiveString, List<CaseInsensitiveString>> targets = specDAG.get(cisrc);
if (targets == null) {
return; // should never happen for valid s-t/v
}
List<CaseInsensitiveString> variants = targets.get(citrg);