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
* argument false if a client wants to abort a cancel action.
     */
    public void setCanceled(boolean b) {
        fIsCanceled = b;
        if (fCancelButton != null)
            fCancelButton.setEnabled(!b);
    }
    /**
     * Controls whether the ProgressIndication provides UI for canceling
     * a long running operation.
     * If the ProgressIndication is currently visible calling this method may have
     * a direct effect on the layout because it will make a cancel button visible. 
     */
    public void setCancelEnabled(boolean enabled) {
        fCancelEnabled = enabled;
        if (fProgressIsVisible && !fCancelButtonIsVisible && enabled) {
            showButton();
            layout();
        }
        if (fCancelButton != null && !fCancelButton.isDisposed())
            fCancelButton.setEnabled(enabled);
    }
    /**
     * Sets the error message text to be displayed on the status line.
     * The image on the status line is cleared.
     * 
     * @param message the error message, or <code>null</code> for no error message
     */
    public void setErrorMessage(String message) {
        setErrorMessage(null, message);