fix error handling in item.save().

When item.save(callbackFn) is called with invalid input, the server rejects the request with a 400 response, as expected. The client, however, does not call the given callbackFn to provide the error to the caller. Instead, an uncaught error is thrown trying to wrap the `null` data into a collection.

This fixes the problem by only wrapping non-`null` response `data`.

Author: jonathanstokes

lib/CollectionItem.js

@@ -23,7 +23,7 @@
 
 		this.save = function(saveCallback) {
 			restHandlers.editItem(data.id, kind, changedData, function (error, data, additionalData, req, res) {
-				var collectionItems = wrapCollectionItems([data], kind, options);
+				var collectionItems = wrapCollectionItems(data ? [data] : data, kind, options);
 				saveCallback(error, collectionItems[0], additionalData, req, res);
 			});
 
@@ -41,14 +41,14 @@
 
 		this.merge = function (withId, callback) {
 			return restHandlers.mergeItem(data.id, withId, kind, function (error, data, additionalData, req, res) {
-				var collectionItems = wrapCollectionItems([data], kind, options);
+				var collectionItems = wrapCollectionItems(data ? [data] : data, kind, options);
 				callback(error, collectionItems[0], additionalData, req, res);
 			});
 		};
 
 		this.duplicate = function (callback) {
 			return restHandlers.duplicateItem(data.id, kind, function (error, data, additionalData, req, res) {
-				var collectionItems = wrapCollectionItems([data], kind, options);
+				var collectionItems = wrapCollectionItems(data ? [data] : data, kind, options);
 				callback(error, collectionItems[0], additionalData, req, res);
 			});
 		};