Customers data is null in backend listing(Shopware 6)

I am developing a plugin for shopware 6

I have created a table with the name “hatslogic_abandoned_cart_items”. Then I have created the definition, entity, and collection classes for the table.

I need a backend listing for this table. so I created the backend Vuejs files and my listing is working fine. (Backend listing API URL is http://localhost:8000/api/v1/search/hatslogic-abandoned-cart-items). But in the response the is null. I want to show the customer name in the listing. I have added 

new ManyToOneAssociationField('customer', 'customer_id', CustomerDefinition::class, 'id', false),

This code in my definition class.

Do I need anything else? I have checked the table the customer id is present in both “hatslogic_abandoned_cart_items” table and “customers” table

what I have to do?