Bug 335308 [JFace] JavaDoc of ControlDecoration#setDescriptionText is wrong
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/ControlDecoration.java
if (!visible) {
			return;
		}
		
		
		if (text == null || text.length() == 0) {
			hideHover();
			return;
		}
		
		
		
		if (hover == null) {
			hover = new Hover(hoverNear.getShell());
		}
		hover.setText(text, getDecorationRectangle(control.getParent()),
				control);
		hover.setVisible(true);
	}
	/*
	 * Remove any listeners installed on the controls.
	 */
	private void removeControlListeners() {
		if (control == null) {
			return;
		}
		printRemoveListener(control, "FOCUS"); 
		control.removeFocusListener(focusListener);
		focusListener = null;