Bug 140160 [Field Assist] - JAVADOC ONLY- FieldDecorationRegistry API should specify that null dec description is allowed
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/FieldDecorationRegistry.java
FieldDecoration getDecoration() {
			if (decoration == null) {
				if (image == null) {
					if (imageRegistry == null) {
						imageRegistry = JFaceResources.getImageRegistry();
					}
					image = imageRegistry.get(imageId);
				}
				decoration = new FieldDecoration(image, description);
			}
			
			description = null;
			imageId = null;
			imageRegistry = null;
			image = null;
			return decoration;
		}
	}
	/**
	 * Default instance of the registry. Applications may install their own
	 * registry.
	 */
	private static FieldDecorationRegistry defaultInstance;
	/**
	 * Maximum width and height used by decorations in this registry. Clients
	 * may use these values to reserve space in dialogs for decorations or to
	 * adjust layouts so that decorated and non-decorated fields line up.
	 */
	private int maxDecorationWidth, maxDecorationHeight;
	private HashMap decorations = new HashMap();