void mergeGroup(Group sourceGroup, ProgramFragment destFragment)
			throws NotFoundException, NotEmptyException {
		if (sourceGroup instanceof ProgramFragment) {
			mergeFragments((ProgramFragment) sourceGroup, destFragment);
		}
		else {
			flattenModule((ProgramModule) sourceGroup, destFragment);
		}
	}
If sourceGroup is a Fragment, then merge code units from it into
destFragment. Otherwise, flatten the source module by moving all
descendant fragments' code units into destFragment.
@param sourceGroup group that is source for the merge
@param destFragment destination fragment where all code units
will end up
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/programtree/ProgramDnDTree.java