JSON converter improvement. Part 2

Pull Request description

[ ] You have reviewed the guidelines document.
[ ] Labels that classify your pull request have been added.
[ ] The milestone is specified and corresponds to fix version.
[ ] Description references specific issue.
[ ] Description contains human-readable scope of changes.
[ ] Description contains brief notes about what needs to be added to the documentation.
[ ] No merge conflicts, commented blocks of code, code formatting issues.
[ ] Changes are backward compatible or upgrade script is provided.
[ ] Similar PR is opened for PE version to simplify merge. Crosslinks between PRs added. Required for internal contributors only.

[ ] Screenshots with affected component(s) are added. The best option is to provide 2 screens: before and after changes;
[ ] If you change the widget or other API, ensure it is backward-compatible or upgrade script is present.
[ ] Ensure new API is documented here

[ ] Added corresponding unit and/or integration test(s). Provide written explanation in the PR description if you have failed to add tests.
[ ] If new dependency was added: the dependency tree is checked for conflicts.
[ ] If new service was added: the service is marked with corresponding @TbCoreComponent, @TbRuleEngineComponent, @TbTransportComponent, etc.
[ ] If new REST API was added: the RestClient.java was updated, issue for Python REST client is created.
[ ] If new yml property was added: make sure a description is added (above or near the property).