WW-4533 Reverts the old behaviour of how empty action should be handled

apps/rest-showcase/src/main/java/org/demo/rest/example/IndexController.java

@@ -0,0 +1,16 @@
+package org.demo.rest.example;
+
+import org.apache.struts2.convention.annotation.Action;
+import org.apache.struts2.convention.annotation.Result;
+import org.apache.struts2.convention.annotation.Results;
+
+@Results({
+    @Result(name="success", type="redirectAction", params = {"actionName" , "orders"})
+})
+public class IndexController {
+
+    @Action("/")
+    public String index() {
+        return "success";
+    }
+}

plugins/rest/src/main/java/org/apache/struts2/rest/RestActionMapper.java

@@ -283,18 +283,16 @@ public ActionMapping getMapping(HttpServletRequest request,
             if (id != null) {
                 if (!"new".equals(id)) {
                     if (mapping.getParams() == null) {
-                        mapping.setParams(new HashMap());
+                        mapping.setParams(new HashMap<String, Object>());
                     }
                     mapping.getParams().put(idParameterName, new String[]{id});
                 }
                 fullName = fullName.substring(0, lastSlashPos);
             }
 
             mapping.setName(fullName);
-            return mapping;
         }
-        // if action name isn't specified, it can be a normal request, to static resource, return null to allow handle that case
-        return null;
+        return mapping;
     }
 
     private void handleDynamicMethodInvocation(ActionMapping mapping, String name) {

plugins/rest/src/test/java/org/apache/struts2/rest/RestActionMapperTest.java

@@ -63,7 +63,7 @@ public void testRootMapping() throws Exception {
 
         ActionMapping mapping = mapper.getMapping(req, configManager);
 
-        assertNull(mapping);
+        assertNotNull(mapping);
     }
 
     public void testGetMapping() throws Exception {