Prevent 404 in .../contextMenu link when there's no context menu

core/src/main/java/hudson/Functions.java

@@ -58,6 +58,7 @@ import hudson.views.ViewsTabBar;
 import hudson.widgets.RenderOnDemandClosure;
 import jenkins.model.GlobalConfiguration;
 import jenkins.model.Jenkins;
+import jenkins.model.ModelObjectWithContextMenu;
 import org.acegisecurity.providers.anonymous.AnonymousAuthenticationToken;
 import org.apache.commons.jelly.JellyContext;
 import org.apache.commons.jelly.JellyTagException;
@@ -146,6 +147,10 @@ public class Functions {
         return o instanceof ModelObject;
     }
 
+    public static boolean isModelWithContextMenu(Object o) {
+        return o instanceof ModelObjectWithContextMenu;
+    }
+
     public static String xsDate(Calendar cal) {
         return Util.XS_DATETIME_FORMATTER.format(cal.getTime());
     }