i am having this rest query

https://XXX.salesforce.com/services/data/v45.0/query?q=SELECT id,name,Phone,accountNumber,industry, (SELECT Contact.Name FROM AccountContactRoles WHERE IsPrimary = TRUE) FROM account

this returns data:

{

      "attributes": {

        "type": "Account",

        "url": "/services/data/v45.0/sobjects/Account/0016g000006hPozAAE"

      },

      "Id": "0016g000006hPozAAE",

      "Name": "Dean Infotech",

      "Phone": null,

      "AccountNumber": null,

      "Industry": "Technology",

      "AccountContactRoles": null

    },

The AccountContactRoles shows null which i am not sure why?  if i go to the above account i can see a contact is added under contact roles and it shows as primary. 

Please advise