Fix boolean casting for nil value

What does this MR do?

nil value is not included in ActiveModel::Type::Boolean::FALSE_VALUES which caused that in Rails 5 the boolean_accessor converted nil to true instead of false.

(https://stackoverflow.com/questions/16848052/value-to-boolean-deprecated-whats-a-good-replacement/25514105#25514105)

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #46925 (closed)