Bug 53881 [Colors] Color/Gradient registry should return default values.
There should be default values for when a user does .get() on a bad key.
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/GradientRegistry.java
*/
	private Gradient createGradient(String symbolicName, GradientData data) {
		return new Gradient(display, data);
	}
	/**
	 * Dispose of all of the <code>Gradient</code>s in this iterator.
	 * 
	 * @param Iterator over <code>Collection</code> of <code>Gradient</code>
	 */
	private void disposeGradients(Iterator iterator) {
		while (iterator.hasNext()) {
			Object next = iterator.next();
			((Gradient) next).dispose();
		}
	}
	/**
	 * Returns the <code>gradient</code> associated with the given symbolic gradient 
	 * name, or <code>null</code> if no such definition exists.
	 * 
	 * @param symbolicName symbolic gradient name.
	 * @return the <code>Gradient</code>.
	 */
	public Gradient get(String symbolicName) {
		Assert.isNotNull(symbolicName);
		Object result = stringToGradient.get(symbolicName);
		if (result != null)
			return (Gradient) result;
		result = stringToGradientData.get(symbolicName);
		if (result == null)
			return null;