parse virtual-host-gatherer null value

[mbussolotto]

What does this PR change?

parse virtual-host-gatherer null value.
Fix for Virtual host manager web UI cucumber tests

GUI diff

Before:

• DONE

Documentation

• No documentation needed
• DONE

Test coverage

• Unit tests were added

• DONE

Links

• DONE

Changelogs

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[github-actions]

Suggested tests to cover this Pull Request

• srv_virtual_host_manager
• buildhost_docker_auth_registry
• srv_menu
• buildhost_docker_build_image
• buildhost_osimage_build_image

[mbussolotto]

@cbosdo it seems that 5a6ca6c is not enough to parse null value. I also added unit test. Let me know what you think about it ;)

[cbosdo]

LGTM