Fix missing code_version in payload and don't set optional fields if …

[diegov]

Description of the change

This PR fixes the missing code_version field in the payload, if provided.

It also updates other optional fields so that they're only added to the payload if they are not null.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

Related issues

• Fix [ch90062]

Checklists

Development

• Lint rules pass locally
• The code changed/added as part of this pull request has been covered with tests
• All tests related to the changed code pass in development

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• "Ready for review" label attached to the PR and reviewers assigned
• Issue from task tracker has a link to this pull request
• Changes have been reviewed by at least one other engineer

[shortcut-integration]

This pull request has been linked to Clubhouse Story #90062: rollbar-flutter: missing code_version in payload.