Passing Object to a Class

Question

I hate to ask a simple thing like this but I've tried to read all the posts that I can find on the subject.

I'm fairly new to C# programming and I'm stuck at how to pass an Object I've created to a class that needs to take care of the handling of the data.

So, I'm populating my object with data and pass the object to my class safe.serializeObject.

            BaseSafeItem myItem = new BaseSafeItem();
            myItem.Title = itemTitle.Text;
            myItem.Content = itemContent.Text;
            myItem.IsProtected = (string.IsNullOrEmpty(itemPassword.Text)) ? false : true;

            string newItemSer = safe.serailizeObject(myItem);

The class should the serialize the object and pass it back as a string, and this is not a problem if I do it inline.

       public string serailizeObject(object obj)
        {
            
            MemoryStream ms = new MemoryStream();

            DataContractJsonSerializer serItem = new DataContractJsonSerializer(typeof(BaseSafeItem));
            serItem.WriteObject(ms, obj);
            byte[] json = ms.ToArray();

            return Encoding.UTF8.GetString(json, 0, json.Length);
        }

 But the object can't be passed on and I get an error saying

An exception of type 'System.NullReferenceException' occurred

Additional information: Object reference not set to an instance of an object.

How should I pass this object over to my class to handle the serialization of it?