Fixes U4-1784

src/Umbraco.Web/Strategies/DataTypes/LegacyUploadFieldWorkaround.cs

@@ -57,6 +57,10 @@ namespace Umbraco.Web.Strategies.DataTypes
 			if (uploadFieldConfigNode != null)
 			{
 				var fileSystem = FileSystemProviderManager.Current.GetFileSystemProvider<MediaFileSystem>();
+                //Ensure that the Property has a Value before continuing
+                if(property.Value == null)
+                    return;
+
 				var path = fileSystem.GetRelativePath(property.Value.ToString());
 
 				if (string.IsNullOrWhiteSpace(path) == false && fileSystem.FileExists(path))

src/umbraco.cms/businesslogic/datatype/FileHandlerData.cs

@@ -123,6 +123,9 @@ namespace umbraco.cms.businesslogic.datatype
 
         private void ClearRelatedValues()
         {
+            if(PropertyId == default(int))
+                return;
+
             string propertyTypeAlias = new Property(PropertyId).PropertyType.Alias;
             if (UmbracoSettings.ImageAutoFillImageProperties != null)
             {