Trying to fix an NPE found in my logs.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@8155 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/model/Hudson.java

@@ -1964,7 +1964,7 @@ public final class Hudson extends View implements ItemGroup<TopLevelItem>, Node,
      */
     public void doIconSize( StaplerRequest req, StaplerResponse rsp ) throws IOException, ServletException {
         String qs = req.getQueryString();
-        if(!ICON_SIZE.matcher(qs).matches())
+        if(qs==null || !ICON_SIZE.matcher(qs).matches())
             throw new ServletException();
         Cookie cookie = new Cookie("iconSize", qs);
         cookie.setMaxAge(/* ~4 mo. */9999999); // #762