dropped noaction in favor of literal null

Core/src/org/sleuthkit/autopsy/commonfilesearch/NoAction.java

@@ -1,38 +0,0 @@
-/*
- * 
- * Autopsy Forensic Browser
- * 
- * Copyright 2018 Basis Technology Corp.
- * Contact: carrier <at> sleuthkit <dot> org
- * 
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- * 
- *     http://www.apache.org/licenses/LICENSE-2.0
- * 
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-package org.sleuthkit.autopsy.commonfilesearch;
-
-import java.awt.event.ActionEvent;
-import javax.swing.AbstractAction;
-
-/**
- * Default action for nodes which do not represent files, such as 
- * <code>InstanceCountNode</code> and <code>Md5Node</code>.
- */
-public class NoAction extends AbstractAction {
-
-    private static final long serialVersionUID = 1L;
-
-    @SuppressWarnings("PMD")
-    @Override
-    public void actionPerformed(ActionEvent e) {
-        //intentionally does nothing
-    }
-}

Core/src/org/sleuthkit/autopsy/directorytree/DataResultFilterNode.java

@@ -41,7 +41,6 @@ import org.sleuthkit.autopsy.actions.AddBlackboardArtifactTagAction;
 import org.sleuthkit.autopsy.actions.AddContentTagAction;
 import org.sleuthkit.autopsy.actions.DeleteFileBlackboardArtifactTagAction;
 import org.sleuthkit.autopsy.actions.DeleteFileContentTagAction;
-import org.sleuthkit.autopsy.commonfilesearch.NoAction;
 import org.sleuthkit.autopsy.core.UserPreferences;
 import org.sleuthkit.autopsy.coreutils.ContextMenuExtensionPoint;
 import org.sleuthkit.autopsy.coreutils.Logger;
@@ -532,17 +531,17 @@ public class DataResultFilterNode extends FilterNode {
 
         @Override 
         public AbstractAction visit(InstanceCountNode icn){
-            return new NoAction();
+            return null;
         }
         
         @Override
         public AbstractAction visit(Md5Node md5n){
-            return new NoAction();
+            return null;
         }
         
         @Override
         public AbstractAction visit(FileInstanceNode fin){
-            return new NoAction();
+            return null;
         }
         
         @Override