Enhancement/category export without parent

Handle properly category which doesn't have parent mapped

| Q                   | A
| ------------------- | ---
| Bug fix?            | y
| New feature?        | n
| BC breaks?          | n
| Tests pass?         | y
| Scenarios pass?     | y
| Checkstyle issues?  | n
| Changelog updated?  | y
| Fixed tickets       | 
| Doc PR              |
| Related CE PR       |