Bug 184423 [JFace] ColorRegistry.getRGB(String) can return null
I20070427-0010 ColorRegistry.getRGB(String) can return null but this is not speced in the Javadoc.
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ColorRegistry.java
/**
     * Returns the color data associated with the given symbolic color name.
     *
     * @param symbolicName symbolic color name.
     * @return the <code>RGB</code> data.
     */
    public RGB getRGB(String symbolicName) {
        Assert.isNotNull(symbolicName);
        return (RGB) stringToRGB.get(symbolicName);
    }
    
    /**
     * Returns the color descriptor associated with the given symbolic color name.
     * @since 3.1 
     *
     * @param symbolicName
     * @return the color descriptor associated with the given symbolic color name.
     */
    public ColorDescriptor getColorDescriptor(String symbolicName) {
        return ColorDescriptor.createFrom(getRGB(symbolicName));
    }
    /* (non-Javadoc)
     * @see org.eclipse.jface.resource.ResourceRegistry#clearCaches()
     */
    protected void clearCaches() {
        disposeColors(stringToColor.values().iterator());
        disposeColors(staleColors.iterator());
        stringToColor.clear();
        staleColors.clear();
    }