Handle null values in watch node/preview bubble (#13855)

* Handle null values in watch node/preview bubble

* Add test

* Update WatchNodeTests.cs

(cherry picked from commit b1bc7c2)

# Conflicts:
#	test/DynamoCoreWpfTests/WatchNodeTests.cs

src/DynamoCoreWpf/ViewModels/Preview/WatchViewModel.cs

@@ -249,6 +249,9 @@ public WatchViewModel(string label, string path, Action<string> tagGeometry, boo
 
         private static string GetStringFromObject(object obj)
         {
+            if (obj == null)
+                return Resources.NullString;
+
             TypeCode type = Type.GetTypeCode(obj.GetType());
             switch (type)
             {
@@ -285,6 +288,9 @@ private static string ObjectToLabelString(object obj)
 
         private string GetDisplayType(object obj)
         {
+            if (obj == null)
+                return Resources.NullString;
+
             TypeCode typeCode = Type.GetTypeCode(obj.GetType());
             // returning a customized user friendly string instead of just returning the name of the type 
             switch (typeCode)

test/DynamoCoreWpfTests/WatchNodeTests.cs

@@ -256,6 +256,29 @@ public void WatchNestedDictionary()
             Assert.AreEqual(2, watchVM.NumberOfItems);
         }
 
+        [Test]
+        public void WatchDictionary()
+        {
+            string openPath = Path.Combine(TestDirectory, @"core\watch\WatchDictionary.dyn");
+            ViewModel.OpenCommand.Execute(openPath);
+            ViewModel.HomeSpace.Run();
+
+            var watchNode = ViewModel.Model.CurrentWorkspace.NodeFromWorkspace("daa19ed1-36b0-4586-ae11-6470e7c196bd") as Watch;
+
+            var watchVM = GetWatchViewModel(watchNode);
+
+            Assert.AreEqual(3, watchVM.Children.Count);
+
+            Assert.AreEqual("1", watchVM.Children.ElementAt(0).NodeLabel);
+            Assert.AreEqual("Int64", watchVM.Children.ElementAt(0).ValueType);
+
+            Assert.AreEqual("null", watchVM.Children.ElementAt(1).NodeLabel);
+            Assert.AreEqual("null", watchVM.Children.ElementAt(1).ValueType);
+
+            Assert.AreEqual("null", watchVM.Children.ElementAt(2).NodeLabel);
+            Assert.AreEqual("String", watchVM.Children.ElementAt(2).ValueType);
+        }
+
         [Test]
         public void WatchNumber()
         {

test/core/watch/WatchDictionary.dyn

@@ -0,0 +1,144 @@
+{
+  "Uuid": "b3971a38-9e42-4229-9ebd-7fa012a6ac9b",
+  "IsCustomNode": false,
+  "Description": "",
+  "Name": "WatchDictionary",
+  "ElementResolver": {
+    "ResolutionMap": {
+      "DesignScript.Builtin.Dictionary": {
+        "Key": "DesignScript.Builtin.Dictionary",
+        "Value": "DesignScriptBuiltin.dll"
+      }
+    }
+  },
+  "Inputs": [],
+  "Outputs": [],
+  "Nodes": [
+    {
+      "ConcreteType": "Dynamo.Graph.Nodes.CodeBlockNodeModel, DynamoCore",
+      "Id": "275d5ff387254cfa9ff92fac8f2d0e11",
+      "NodeType": "CodeBlockNode",
+      "Inputs": [],
+      "Outputs": [
+        {
+          "Id": "1b7713c8f66d4e38933b4fb97acc7a28",
+          "Name": "",
+          "Description": "Value of expression at line 1",
+          "UsingDefaultValue": false,
+          "Level": 2,
+          "UseLevels": false,
+          "KeepListStructure": false
+        }
+      ],
+      "Replication": "Disabled",
+      "Description": "Allows for DesignScript code to be authored directly",
+      "Code": "{\"a\":1, \"b\": \"null\", \"c\": null};"
+    },
+    {
+      "ConcreteType": "CoreNodeModels.Watch, CoreNodeModels",
+      "Id": "daa19ed136b04586ae116470e7c196bd",
+      "NodeType": "ExtensionNode",
+      "Inputs": [
+        {
+          "Id": "7ce251e0efc946ce85c17be979c34247",
+          "Name": "",
+          "Description": "Node to show output from",
+          "UsingDefaultValue": false,
+          "Level": 2,
+          "UseLevels": false,
+          "KeepListStructure": false
+        }
+      ],
+      "Outputs": [
+        {
+          "Id": "7cbf667c84fa4df3a7d6983d5a2e5825",
+          "Name": "",
+          "Description": "Node output",
+          "UsingDefaultValue": false,
+          "Level": 2,
+          "UseLevels": false,
+          "KeepListStructure": false
+        }
+      ],
+      "Replication": "Disabled",
+      "Description": "Visualizes a node's output"
+    }
+  ],
+  "Connectors": [
+    {
+      "Start": "1b7713c8f66d4e38933b4fb97acc7a28",
+      "End": "7ce251e0efc946ce85c17be979c34247",
+      "Id": "b903a06b6a534010862862dc48bd30b8",
+      "IsHidden": "False"
+    }
+  ],
+  "Dependencies": [],
+  "NodeLibraryDependencies": [],
+  "Thumbnail": "",
+  "GraphDocumentationURL": null,
+  "ExtensionWorkspaceData": [
+    {
+      "ExtensionGuid": "28992e1d-abb9-417f-8b1b-05e053bee670",
+      "Name": "Properties",
+      "Version": "2.18",
+      "Data": {}
+    }
+  ],
+  "Author": "",
+  "Linting": {
+    "activeLinter": "None",
+    "activeLinterId": "7b75fb44-43fd-4631-a878-29f4d5d8399a",
+    "warningCount": 0,
+    "errorCount": 0
+  },
+  "Bindings": [],
+  "View": {
+    "Dynamo": {
+      "ScaleFactor": 1.0,
+      "HasRunWithoutCrash": true,
+      "IsVisibleInDynamoLibrary": true,
+      "Version": "2.18.0.2986",
+      "RunType": "Automatic",
+      "RunPeriod": "1000"
+    },
+    "Camera": {
+      "Name": "_Background Preview",
+      "EyeX": -17.0,
+      "EyeY": 24.0,
+      "EyeZ": 50.0,
+      "LookX": 12.0,
+      "LookY": -13.0,
+      "LookZ": -58.0,
+      "UpX": 0.0,
+      "UpY": 1.0,
+      "UpZ": 0.0
+    },
+    "ConnectorPins": [],
+    "NodeViews": [
+      {
+        "Id": "275d5ff387254cfa9ff92fac8f2d0e11",
+        "Name": "Code Block",
+        "IsSetAsInput": false,
+        "IsSetAsOutput": false,
+        "Excluded": false,
+        "ShowGeometry": true,
+        "X": 220.5,
+        "Y": 325.0
+      },
+      {
+        "Id": "daa19ed136b04586ae116470e7c196bd",
+        "Name": "Watch",
+        "IsSetAsInput": false,
+        "IsSetAsOutput": false,
+        "Excluded": false,
+        "ShowGeometry": true,
+        "X": 656.5,
+        "Y": 399.0
+      }
+    ],
+    "Annotations": [],
+    "X": 0.0,
+    "Y": 0.0,
+    "Zoom": 1.0
+  }
+}