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
private final StatusLineLayoutData DEFAULT_DATA = new StatusLineLayoutData();
        public Point computeSize(Composite composite, int wHint, int hHint,
                boolean changed) {
            if (wHint != SWT.DEFAULT && hHint != SWT.DEFAULT)
                return new Point(wHint, hHint);
            Control[] children = composite.getChildren();
            int totalWidth = 0;
            int maxHeight = 0;
            int totalCnt = 0;
            for (int i = 0; i < children.length; i++) {
                boolean useWidth = true;
                Control w = children[i];
                if (w == fProgressBarComposite && !fProgressIsVisible)
                    useWidth = false;
                else if (w == fToolBar && !fCancelButtonIsVisible)
                    useWidth = false;
                StatusLineLayoutData data = (StatusLineLayoutData) w
                        .getLayoutData();
                if (data == null)
                    data = DEFAULT_DATA;
                Point e = w.computeSize(data.widthHint, data.heightHint,
                        changed);
                if (useWidth) {
                    totalWidth += e.x;
                    totalCnt++;
                }
                maxHeight = Math.max(maxHeight, e.y);
            }
            if (totalCnt > 0)