Bug 63223 Use null to clear message text instead of empty string
I200405200800 StatusLine in jface uses setMessage("") to clear the text while the documentation says you should uset setMessage(null) to clear the text. The code path is slightly different for "" versus null, but using null makes the intent of the caller clearer.
bundles/org.eclipse.jface/src/org/eclipse/jface/action/StatusLine.java
public static final int DELAY_PROGRESS = 500;
    
    protected boolean fProgressIsVisible = false;
    protected boolean fCancelButtonIsVisible = false;
    protected boolean fCancelEnabled = false;
    protected String fTaskName;
    protected boolean fIsCanceled;
    protected long fStartTime;
    private Cursor fStopButtonCursor;
    protected String fMessageText;
    protected Image fMessageImage;
    protected String fErrorText;
    protected Image fErrorImage;
    
    protected CLabel fMessageLabel;
    protected Composite fProgressBarComposite;
    protected ProgressIndicator fProgressBar;
    protected ToolBar fToolBar;
    protected ToolItem fCancelButton;
    protected static ImageDescriptor fgStopImage = ImageDescriptor
            .createFromFile(StatusLine.class, "images/stop.gif");
    static {
        JFaceResources.getImageRegistry().put(
                "org.eclipse.jface.parts.StatusLine.stopImage", fgStopImage);
    }
    /**
     * Layout the contribution item controls on the status line.
     */
    public class StatusLineLayout extends Layout {