Bug 51110 [Preferences] Error notifying a preference listener on font change.
M6 Create a font definition with no defaultsTo attribute. Go in to preferences and change the value of Text Font and hit OK you will get an error because you try call JFaceResources.getFontRegistry().put() with a null value.
bundles/org.eclipse.ui/src/org/eclipse/ui/internal/UIPlugin.java
*
	 * @see AbstractPlugin for the typical implementation pattern for plugin classes.
	 */
	public static UIPlugin getDefault() {
		return inst;
	}
	/** 
	 * Set default preference values.
	 * This method must be called whenever the preference store is initially loaded
	 * because the default values are not stored in the preference store.
	 */
	protected void initializeDefaultPreferences(IPreferenceStore store) {
		
		store.setDefault(IWorkbenchPreferenceConstants.OPEN_NEW_PERSPECTIVE, IWorkbenchPreferenceConstants.OPEN_PERSPECTIVE_REPLACE);
		
		store.setDefault(IWorkbenchPreferenceConstants.PROJECT_OPEN_NEW_PERSPECTIVE, IWorkbenchPreferenceConstants.OPEN_PERSPECTIVE_REPLACE);
		store.setDefault(IWorkbenchPreferenceConstants.SHIFT_OPEN_NEW_PERSPECTIVE, IWorkbenchPreferenceConstants.OPEN_PERSPECTIVE_REPLACE);
		store.setDefault(IWorkbenchPreferenceConstants.ALTERNATE_OPEN_NEW_PERSPECTIVE, IWorkbenchPreferenceConstants.OPEN_PERSPECTIVE_REPLACE);
		
		 
		 
		 
		
		
		store.setDefault(IWorkbenchPreferenceConstants.LINK_NAVIGATOR_TO_EDITOR, false);
		
		store.addPropertyChangeListener(new PlatformUIPreferenceListener());
	}
	}