Add empty recognizer support for CrosstrainedRecognizer (composer scenario)

libraries/Microsoft.Bot.Builder.Dialogs.Adaptive/Recognizers/CrossTrainedRecognizerSet.cs

@@ -79,6 +79,14 @@ public override async Task<RecognizerResult> RecognizeAsync(DialogContext dialog
                 throw new ArgumentNullException(nameof(activity));
             }
 
+            if (Recognizers.Any() == false)
+            {
+                return new RecognizerResult()
+                {
+                    Intents = new Dictionary<string, IntentScore>() { { NoneIntent, new IntentScore() { Score = 1.0 } } }
+                };
+            }
+
             EnsureRecognizerIds();
 
             // run all of the recognizers in parallel

tests/Microsoft.Bot.Builder.Dialogs.Adaptive.Tests/CrossTrainedRecognizerSetTests.cs

@@ -52,5 +52,11 @@ public async Task CrossTrainedRecognizerSetTests_AllNone()
         {
             await TestUtils.RunTestScript(ResourceExplorer);
         }
+
+        [TestMethod]
+        public async Task CrossTrainedRecognizerSetTests_Empty()
+        {
+            await TestUtils.RunTestScript(ResourceExplorer);
+        }
     }
 }

tests/Microsoft.Bot.Builder.Dialogs.Adaptive.Tests/Tests/CrossTrainedRecognizerSetTests/CrossTrainedRecognizerSetTests_Empty.test.dialog

@@ -0,0 +1,52 @@
+{
+    "$schema": "../../../tests.schema",
+    "$kind": "Microsoft.Test.Script",
+    "dialog": {
+        "$kind": "Microsoft.AdaptiveDialog",
+        "recognizer": {
+            "$schema": "../../../tests.schema",
+            "$kind": "Microsoft.CrossTrainedRecognizerSet",
+            "recognizers": [
+            ]
+        },
+        "triggers": [
+            {
+                "$kind": "Microsoft.OnUnknownIntent",
+                "actions": [
+                    {
+                        "$kind": "Microsoft.SendActivity",
+                        "activity": "UnknownIntent:${turn.recognized.intent}"
+                    }
+                ]
+            }
+        ],
+        "defaultResultProperty": "dialog.result"
+    },
+    "locale": "",
+    "script": [
+        {
+            "$kind": "Microsoft.Test.UserSays",
+            "text": "hi"
+        },
+        {
+            "$kind": "Microsoft.Test.AssertReply",
+            "text": "UnknownIntent:None"
+        },
+        {
+            "$kind": "Microsoft.Test.UserSays",
+            "text": "x"
+        },
+        {
+            "$kind": "Microsoft.Test.AssertReply",
+            "text": "UnknownIntent:None"
+        },
+        {
+            "$kind": "Microsoft.Test.UserSays",
+            "text": "y"
+        },
+        {
+            "$kind": "Microsoft.Test.AssertReply",
+            "text": "UnknownIntent:None"
+        }
+    ]
+}