Comment examples of when findListItemInfo can return undefined

src/services/signatureHelp.ts

@@ -227,7 +227,11 @@ module ts.SignatureHelp {
             }
 
             // findListItemInfo can return undefined if we are not in parent's argument list
-            // or type argument list.
+            // or type argument list. This includes cases where the cursor is:
+            //   - To the right of the closing paren
+            //   - Between the type arguments and the arguments (greater than token)
+            //   - On the target of the call (parent.func)
+            //   - On the 'new' keyword in a 'new' expression
             return findListItemInfo(node);
         }