Changed the parameter name to "pageId"

This follows our approach in Stacked Content and gives the intent it for the Page, rather than a "node",
(which becomes confusing in this modern NC/DTGE/StackedContent world)

Added an additional check that the page ID is greater than 0.
A newly created page has an ID of -1, which means that it isn't in the cache or database and would throw an exception.

Author: leekelleher

src/Our.Umbraco.DocTypeGridEditor/Web/Controllers/DocTypeGridEditorApiController.cs

@@ -94,17 +94,23 @@ public object GetDataTypePreValues(string dtdId)
         }
 
         [HttpPost]
-        public HttpResponseMessage GetPreviewMarkup([FromBody] FormDataCollection item, [FromUri] int nodeId)
+        public HttpResponseMessage GetPreviewMarkup([FromBody] FormDataCollection item, [FromUri] int pageId)
         {
-            // Get page container node
-            var page = UmbracoContext.ContentCache.GetById(nodeId);
-            if (page == null)
+            var page = default(IPublishedContent);
+
+            // If the page is new, then the ID will be zero
+            if (pageId > 0)
             {
-                // If unpublished, then fake PublishedContent (with IContent object)
-                page = new UnpublishedContent(nodeId, Services);
+                // Get page container node
+                page = UmbracoContext.ContentCache.GetById(pageId);
+                if (page == null)
+                {
+                    // If unpublished, then fake PublishedContent (with IContent object)
+                    page = new UnpublishedContent(pageId, Services);
+                }
             }
 
-            var culture = UmbracoContext.Application.Services.ContentService.GetById(nodeId).GetCulture();
+            var culture = UmbracoContext.Application.Services.ContentService.GetById(pageId).GetCulture();
             System.Threading.Thread.CurrentThread.CurrentCulture = culture;
             System.Threading.Thread.CurrentThread.CurrentUICulture = culture;
 

src/Our.Umbraco.DocTypeGridEditor/Web/UI/App_Plugins/DocTypeGridEditor/Js/doctypegrideditor.resources.js

@@ -34,8 +34,8 @@
                     'Failed to retrieve datatypes'
                 );
             },
-            getEditorMarkupForDocTypePartial: function (nodeId, id, editorAlias, contentTypeAlias, value, viewPath, previewViewPath) {
-                var url = umbRequestHelper.convertVirtualToAbsolutePath("~/umbraco/backoffice/DocTypeGridEditorApi/DocTypeGridEditorApi/GetPreviewMarkup?dtgePreview=1&nodeId=" + nodeId);
+            getEditorMarkupForDocTypePartial: function (pageId, id, editorAlias, contentTypeAlias, value, viewPath, previewViewPath) {
+                var url = umbRequestHelper.convertVirtualToAbsolutePath("~/umbraco/backoffice/DocTypeGridEditorApi/DocTypeGridEditorApi/GetPreviewMarkup?dtgePreview=1&pageId=" + pageId);
                 return $http({
                     method: 'POST',
                     url: url,