Fix: Don't treat 0 number as an empty attribute value

[psrok1]

Your checklist for this pull request

• I've read the contributing guideline.
• I've tested my changes by building and running the project, and testing changed functionality (if applicable)
• I've added automated tests for my change (if applicable, optional)
• I've updated documentation to reflect my change (if applicable)

What is the current behaviour?

Mentioned in #907, if we try to set 0 value in JSON/object mode, we get ValidationError as value is considered empty

What is the new behaviour?

The only empty values are "", {}, [], null

Test plan

Covered by automated test

Closing issues