SLING-8170 - Allow Sling servlets to declare a resource super type

* made sure the sling.servlet.resourceSuperType has an empty default value
diff --git a/src/main/java/org/apache/sling/servlets/annotations/SlingServletResourceTypes.java b/src/main/java/org/apache/sling/servlets/annotations/SlingServletResourceTypes.java
index a69f07f..5936ad5 100644
--- a/src/main/java/org/apache/sling/servlets/annotations/SlingServletResourceTypes.java
+++ b/src/main/java/org/apache/sling/servlets/annotations/SlingServletResourceTypes.java
@@ -53,7 +53,7 @@
      * @return the resource super type
      * @see ServletResolverConstants#SLING_SERVLET_RESOURCE_SUPER_TYPE
      */
-    String resourceSuperType();
+    String resourceSuperType() default "";
 
     /**
      * One ore more request URL selectors supported by the servlet. The