Bug 165368 [Viewers] TreePath.getParentPath() should return empty path
TreePath.getParentPath() specifies that it returns null for an empty path. However, it also returns null for a one element path. I think it should return the empty path for a one element path, to be consistent with an empty path representing a root element in a tree.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/TreePath.java
*            path to compare to
	 * @param comparer
	 *            the comparer to use, or <code>null</code> if equals() should
	 *            be used to compare segments
	 * @return whether the given path is a prefix of this path, or the same as
	 *         this path
	 */
	public boolean startsWith(TreePath treePath, IElementComparer comparer) {
		int thisSegmentCount = getSegmentCount();
		int otherSegmentCount = treePath.getSegmentCount();
		if (otherSegmentCount == thisSegmentCount) {
			return equals(treePath, comparer);
		}
		if (otherSegmentCount > thisSegmentCount) {
			return false;
		}
		for (int i = 0; i < otherSegmentCount; i++) {
			Object otherSegment = treePath.getSegment(i);
			if (comparer == null) {
				if (!otherSegment.equals(segments[i])) {
					return false;
				}
			} else {
				if (!comparer.equals(otherSegment, segments[i])) {
					return false;
				}
			}
		}
		return true;
	}