Columns are optional in ColumnSet, we had made then required. (#2001)

Addresses issue #1998

samples/Tests/ColumnSet.Empty.json

@@ -0,0 +1,15 @@
+{
+	"$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
+	"type": "AdaptiveCard",
+	"version": "1.0",
+	"body": [
+		{
+			"type": "TextBlock",
+			"text": "This empty columnset should not prevent the card from rendering"
+		},
+		{
+			"type": "ColumnSet",
+			"columns": []
+		}
+	]
+}

source/shared/cpp/ObjectModel/ColumnSet.cpp

@@ -69,7 +69,7 @@ std::shared_ptr<BaseCardElement> ColumnSetParser::Deserialize(
     auto container = BaseCardElement::Deserialize<ColumnSet>(value);
 
     // Parse Columns
-    auto cardElements = ParseUtil::GetElementCollectionOfSingleType<Column>(elementParserRegistration, actionParserRegistration, warnings, value, AdaptiveCardSchemaKey::Columns, Column::Deserialize, true);
+    auto cardElements = ParseUtil::GetElementCollectionOfSingleType<Column>(elementParserRegistration, actionParserRegistration, warnings, value, AdaptiveCardSchemaKey::Columns, Column::Deserialize, false);
     container->m_columns = std::move(cardElements);
 
     // Parse optional selectAction

source/uwp/AdaptiveCardTestApp/Expected/SourceCards/Tests.ColumnSet.Empty.461f2d5.json

@@ -0,0 +1,15 @@
+{
+	"$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
+	"type": "AdaptiveCard",
+	"version": "1.0",
+	"body": [
+		{
+			"type": "TextBlock",
+			"text": "This empty columnset should not prevent the card from rendering"
+		},
+		{
+			"type": "ColumnSet",
+			"columns": []
+		}
+	]
+}

source/uwp/AdaptiveCardTestApp/Expected/Tests.ColumnSet.EmptyToJson.json

@@ -0,0 +1 @@
+{"actions":[],"body":[{"text":"This empty columnset should not prevent the card from rendering","type":"TextBlock"},{"columns":[],"type":"ColumnSet"}],"type":"AdaptiveCard","version":"1.0"}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.microsoft-teams.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"febd141","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.outlook-desktop.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"04138f4","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.sample.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"45c4c50","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.sampleDifferentFont.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"3e47fb4","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.skype.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"2ac7c52","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.windows-notification.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"e188ab9","CardHash":"461f2d5","Error":null}

source/uwp/AdaptiveCardTestApp/Expected/v1.0.windows-timeline.Tests.ColumnSet.Empty.json

@@ -0,0 +1 @@
+{"HostConfigHash":"e3927b5","CardHash":"461f2d5","Error":null}