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
* Subtasks are optional; the main task might not have subtasks.
     * @param name the name (or description) of the subtask
     * @see IProgressMonitor#subTask(String)
     */
    public void subTask(String name) {
        String text;
        if (fTaskName.length() == 0)
            text = name;
        else
            text = JFaceResources.format(
                    "Set_SubTask", new Object[] { fTaskName, name });
        setMessage(text);
    }
    /**
     * Trims the message to be displayable in the status line.
     * This just pulls out the first line of the message.
     * Allows null.
     */
    String trim(String message) {
        if (message == null)
            return null;
        int cr = message.indexOf('\r');
        int lf = message.indexOf('\n');
        if (cr == -1 && lf == -1)
            return message;
        int len;
        if (cr == -1)
            len = lf;
        else if (lf == -1)
            len = cr;