chore(clients): populate default variant only if hostname exists

[trivikr]

Issue

Improvement noticed while working on #3172

Description

Populate default variant only if hostname exists

Testing

Verified that endpoints tests are successful

$ yarn test:functional
yarn run v1.22.17
$ jest --config tests/functional/jest.config.js
 PASS  tests/functional/signing-names/index.spec.ts
 PASS  tests/functional/endpoints/index.spec.ts

Test Suites: 2 passed, 2 total
Tests:       1506 passed, 1506 total
Snapshots:   0 total
Time:        3.752 s, estimated 7 s
Ran all test suites.
Done in 4.63s.

Additional context

This PR will be made ready once #3172 is merged.

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