XNAT-1612 XNAT-4413 Added check for blank site URL preference setting in

addition to existing no-value check.

src/main/java/org/nrg/xapi/rest/settings/SiteConfigApi.java

@@ -118,7 +118,7 @@ public class SiteConfigApi extends AbstractXapiRestController {
             if (_log.isInfoEnabled()) {
                 _log.info("The site is being initialized by user {}. Setting default values from context.", username);
             }
-            if (!preferences.containsKey("siteUrl")) {
+            if (!preferences.containsKey("siteUrl") || StringUtils.isBlank(preferences.get("siteUrl").toString())) {
                 preferences.put("siteUrl", XnatHttpUtils.getServerRoot(request));
             }
         }