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/FontRegistry.java
/**
	 * Table of known fonts, keyed by symbolic font name
	 * (key type: <code>String</code>, 
	 *  value type: <code>org.eclipse.swt.graphics.Font</code>.
	 */
	private Map stringToFont = new HashMap(7);
	/**
	 * Table of known font data, keyed by symbolic font name
	 * (key type: <code>String</code>, 
	 *  value type: <code>org.eclipse.swt.graphics.FontData[]</code>).
	 */
	private Map stringToFontData = new HashMap(7);
	/**
	 * Collection of Fonts that are now stale to be disposed
	 * when it is safe to do so (i.e. on shutdown).
	 * @see List
	 */
	private List staleFonts = new ArrayList();
	
	/**
	 * Runnable that cleans up the manager on disposal of the display.
	 */	
	protected Runnable displayRunnable = new Runnable() {
		public void run() {
			clearCaches();