- Fix "creator.serialize() is not a function" sync error

- Added Zotero.Utilities.isEmpty(obj)

chrome/content/zotero/xpcom/sync.js

@@ -2452,7 +2452,9 @@ Zotero.Sync.Server.Data = new function() {
 		};
 		
 		if (type == 'item') {
-			io.dataIn.changedCreators = changedCreators;
+			if (!Zotero.Utilities.prototype.isEmpty(changedCreators)) {
+				io.dataIn.changedCreators = changedCreators;
+			}
 		}
 		
 		var wm = Components.classes["@mozilla.org/appshell/window-mediator;1"]

chrome/content/zotero/xpcom/utilities.js

@@ -291,6 +291,20 @@ Zotero.Utilities.prototype.isInt = function(x) {
 }
 
 
+
+/**
+ * Test if an object is empty
+ *
+ * @param	{Object}
+ */
+Zotero.Utilities.prototype.isEmpty = function (obj) {
+    for (var i in obj) {
+        return false;
+    }
+    return true;
+}
+
+
 /**
  * Compares an array with another and returns an array with
  *	the values from array2 that don't exist in array1