Fix #304

app/Umbraco/Umbraco.Archetype/Models/ArchetypeModel.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Linq;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
+using Umbraco.Core.Logging;
 
 namespace Archetype.Models
 {
@@ -47,6 +48,22 @@ namespace Archetype.Models
         /// <returns></returns>
         public string SerializeForPersistence()
         {
+            //clean out any properties with a null datatype
+            foreach (var fieldset in Fieldsets)
+            {
+                var properties = fieldset.Properties.ToList();
+
+                foreach (var property in fieldset.Properties)
+                {
+                    if (property.DataTypeGuid == null)
+                    {
+                        properties.Remove(property);
+                    }
+                }
+
+                fieldset.Properties = properties;
+            }
+
             var json = JObject.Parse(JsonConvert.SerializeObject(this, new JsonSerializerSettings() { ReferenceLoopHandling = ReferenceLoopHandling.Ignore }));
 
             var propertiesToRemove = new String[] { "propertyEditorAlias", "dataTypeId", "dataTypeGuid", "hostContentType", "editorState" };