removes one null check, adds notes

src/Umbraco.Web/PublishedCache/NuCache/ContentStore.cs

@@ -502,6 +502,14 @@ namespace Umbraco.Web.PublishedCache.NuCache
             }
         }
 
+        /// <summary>
+        /// Validate the <see cref="ContentNodeKit"/> and try to create a parent <see cref="LinkedNode{ContentNode}"/>
+        /// </summary>
+        /// <param name="kit"></param>
+        /// <param name="parent"></param>
+        /// <returns>
+        /// Returns false if the parent was not found or if the kit validation failed
+        /// </returns>
         private bool BuildKit(ContentNodeKit kit, out LinkedNode<ContentNode> parent)
         {
             // make sure parent exists

src/Umbraco.Web/PublishedCache/NuCache/Snap/LinkedNode.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace Umbraco.Web.PublishedCache.NuCache.Snap
+namespace Umbraco.Web.PublishedCache.NuCache.Snap
 {
     //NOTE: This cannot be struct because it references itself
 
@@ -13,7 +11,7 @@ namespace Umbraco.Web.PublishedCache.NuCache.Snap
     {
         public LinkedNode(TValue value, long gen, LinkedNode<TValue> next = null)
         {
-            Value = value ?? throw new ArgumentNullException(nameof(value));
+            Value = value; // This is allowed to be null, we actually explicitly set this to null in ClearLocked
             Gen = gen;
             Next = next;
         }