Sharepoint Custom Field default template

Question

Hi all

I want to develop a custom lookup field for sharepoint.

I created a class as the following

public class CustomLookupControl:BaseFieldControl

and overided this method

protected override string DefaultTemplateName
        {
            get
            {
                return base.DefaultTemplateName;                    
            }
        }

but when I edit an item I find that the place of the field is empty.

my question is that I don't want to implement a custom rendering template for the field, I want to use the default template of the lookup field

how can this be achieved.