GraphQL returns null address if optional telephone is set as empty string

Question

Steps to reproduce

1. Using GraphQL mutation, add a product to Cart

2. Set Shipping Addresses on cart using the following Mutation

mutation {
  setShippingAddressesOnCart(
    input: {
      cart_id: "zcatHMtPLY8M8hs0I1ALNihsk8bdRlUI"
      shipping_addresses: [
        {
          address: {
            firstname: "Bob"
            lastname: "Roll"
            company: "Magento"
            street: ["Magento Pkwy", "Main Street"]
            city: "Austin"
            region: "AN"
            region_id: 533
            postcode: "78758"
            country_code: "IN"
            telephone: "" #<---- note that the telephone is an empty string. 
            save_in_address_book: false
          },
       }
      ]
    }
  ) {
    cart {
      shipping_addresses {
        firstname
        lastname
        company
        street
        city
        region {
          code
          label
        }
        postcode
        telephone
        country {
          code
          label
        }
        pickup_location_code
      }
    }
  }
}

Response:

{
  "data": {
    "setShippingAddressesOnCart": {
      "cart": {
        "shipping_addresses": []
      }
    }
  }
}

I've tried few things but they didn't work, Does any knows how to resolve it?

Answer 1

Resolved by adding following schema.graphqls

interface CartAddressInterface @typeResolver(class: "\\Magento\\QuoteGraphQl\\Model\\Resolver\\CartAddressTypeResolver") {
    firstname: String!
    lastname: String!
    company: String
    street: [String!]!
    city: String!
    region: CartAddressRegion
    postcode: String
    country: CartAddressCountry!
    telephone: String
}

input CartAddressInput {
    firstname: String!
    lastname: String!
    company: String
    street: [String!]!
    city: String!
    region: String
    region_id: Int
    postcode: String
    country_code: String!
    telephone: String
    save_in_address_book: Boolean @doc(description: "Determines whether to save the address in the customer's address book. The default value is true")
}