FIO-7823: fixed an issue where the submission of dataGrid with nested form returns server error

Link to Jira Ticket

What changed?

Improved the check inside the isEmpty method of the nested form to work with undefined values.

Manually

[x] I have completed the above PR template
[ ] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation (if applicable)
[x] My changes generate no new warnings
[ ] My changes include tests that prove my fix is effective (or that my feature works as intended)
[x] New and existing unit/integration tests pass locally with my changes
[ ] Any dependent changes have corresponding PRs that are listed above