Medis imp export api fe valid

[evgeny-pluzhnikov]

Description

Convert empty arrays to null when doing multi upload

There is a bug in form.io framework to do with arrays when calling validation defined for the form. The bug exposes itself when you call validation routine more than once (our case in multi upload). The work around for this bug is to replace empty arrays in json payload will null.

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist

• [X] I have read the CONTRIBUTING doc
• [X] I have checked that unit tests pass locally with my changes
• [X] I have run the npm script lint on the frontend and backend
• [X] I have added tests that prove my fix is effective or that my feature works
• [X] I have added necessary documentation (if appropriate)
• [X] I have approval from the product owner for the contribution in this pull request

Further comments