Fixed crash with Digital Form MultiImage fields

InABox.Core/DigitalForms/Layouts/Fields/DFLayoutMultiImage/DFLayoutMultiImageProperties.cs

@@ -5,10 +5,10 @@ using System.Linq;
 
 namespace InABox.Core
 {
-    public class DFLayoutMultiImageProperties : DFLayoutFieldProperties<List<Guid>, DFLayoutEmbeddedMediaValues>
+    public class DFLayoutMultiImageProperties : DFLayoutFieldProperties<List<Guid>?, DFLayoutEmbeddedMediaValues>
     {
 
-        [EditorSequence(-995)] [NullEditor] public override List<Guid> Default { get; set; } = new List<Guid>();
+        [EditorSequence(-995)] [NullEditor] public override List<Guid>? Default { get; set; } = new List<Guid>();
         
         [EditorSequence(100)]
         [CheckBoxEditor]