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
/* (non-Javadoc)
     * @see org.eclipse.jface.resource.ResourceRegistry#hasValueFor(java.lang.String)
     */
    public boolean hasValueFor(String colorKey) {
        return stringToRGB.containsKey(colorKey);
    }
    /**
     * Hook a dispose listener on the SWT display.
     */
    private void hookDisplayDispose() {
        display.disposeExec(displayRunnable);
    }
    /**
     * Adds (or replaces) a color to this color registry under the given 
     * symbolic name.
     * <p>
     * A property change event is reported whenever the mapping from a symbolic
     * name to a color changes. The source of the event is this registry; the
     * property name is the symbolic color name.
     * </p>
     * 
     * @param symbolicName the symbolic color name
     * @param colorData an <code>RGB</code> object
     */
    public void put(String symbolicName, RGB colorData) {
        put(symbolicName, colorData, true);
    }
    /**
     * Adds (or replaces) a color to this color registry under the given 
     * symbolic name.