Resolver produces null when resolver returns a record containing a map of service objects as its field

[MohamedSabthar]

Description:
Consider the following code

import ballerina/graphql;

public service class AccountDetails {
    final string name;
    final int createdYear;

    function init(string name, int createdYear) {
        self.name = name;
        self.createdYear = createdYear;
    }

    resource function get name() returns string {
        return self.name;
    }

    resource function get createdYear() returns int {
        return self.createdYear;
    }
}

public type AccountRecords record {|
    map<AccountDetails> details;
|};

service /graphql on new graphql:Listener(5001) {
    resource function get account() returns AccountRecords {
        return {details: {acc1: new ("James", 2022), acc2: new ("Paul", 2015)}};
    }
}

The above code returning {"data": null}
for the below query

{
  account {
    details(key:"acc1") {
      name
    }
  }
}

The expected value for the above query is

"data": {
    "account": {
        "details": {
            "name": "James"
        }
    }
}

Affected Versions:

OS, DB, other environment details and versions:

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[github-actions]

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      - Reason/EngineeringMistake - The issue occurred due to a mistake made in the past.
      - Reason/Regression - The issue has introduced a regression.
      - Reason/MultipleComponentInteraction - Issue occured due to interactions in multiple components.
      - Reason/Complex - Issue occurred due to complex scenario.
      - Reason/Invalid - Issue is invalid.
      - Reason/Other - None of the above cases.