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
* @param comparer
	 *            comparator to use or <code>null</code> if segments should be
	 *            compared using equals()
	 * @return whether the paths are equal
	 */
	public boolean equals(TreePath otherPath, IElementComparer comparer) {
		if (otherPath == null) {
			return false;
		}
		if (segments.length != otherPath.segments.length) {
			return false;
		}
		for (int i = 0; i < segments.length; i++) {
			if (comparer == null) {
				if (!segments[i].equals(otherPath.segments[i])) {
					return false;
				}
			} else {
				if (!comparer.equals(segments[i], otherPath.segments[i])) {
					return false;
				}
			}
		}
		return true;
	}
	/**
	 * Returns whether this path starts with the same segments as the given
	 * path, using the given comparer to compare segments.
	 * 
	 * @param treePath