Add defensive check in block editor value connector for input that parses as JSON but incudes no content.

Author: AndyButland

src/Umbraco.Deploy.Contrib/ValueConnectors/BlockEditorValueConnector.cs

@@ -1,4 +1,4 @@
-using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 using System;
@@ -69,7 +69,7 @@ public override string ToArtifact(object value, IPropertyType propertyType, ICol
                 return null;
             }
 
-            if (blockEditorValue == null)
+            if (blockEditorValue?.Content == null)
             {
                 _logger.LogWarning("Deserialized value is null. Skipping conversion to artifact.");
                 return null;