Arquillian tests fails when running from Intellij Idea

closes #44713

Signed-off-by: mposolda <mposolda@gmail.com>

services/src/test/java/org/keycloak/utils/JsonConfigProvider.java

@@ -90,7 +90,7 @@ public class JsonConfigProvider implements Config.ConfigProvider {
 
         private String toString(JsonNode n) {
             String v = replaceProperties(n.textValue());
-            return !v.isEmpty() ? v : null;
+            return !StringUtil.isNullOrEmpty(v) ? v : null;
         }
 
         @Override