feat: Save DocumentClient reference to CollectionRef

Author: HomelessDinosaur

Nitric.Sdk/Document/CollectionRef.cs

@@ -26,6 +26,7 @@ namespace Nitric.Api.Document
 
         internal CollectionRef(DocumentServiceClient documentClient, string name, Key<T> parentKey = null)
         {
+            this.documentClient = documentClient;
             this.name = name;
             this.ParentKey = parentKey;
         }

Nitric.Sdk/Document/DocumentRef.cs

@@ -43,8 +43,7 @@ public Document<T> Get()
             DocumentGetRequest request = new DocumentGetRequest();
             request.Key = this.Key.ToKey();
 
-            DocumentGetResponse response = null;
-            response = this.documentClient.Get(request);
+            var response = this.documentClient.Get(request);
 
             return new Document<T>(
                 this,