Connection with issue(s)

Close #473

Solution description

Allow null values for CompareValidator.

Use case example: a shopping application. User can specify price range to search for matching products. If either min or max prices are null, that's fine - this side of the search filter won't be limited. But if both are specified, a validation is needed (expected: min <= max).

Possible workarounds for this functionality are verbose:

• either a CompareValidator should be duplicated as a custom validator (allowing nulls)
• or composeOR can be used in combination with a custom AllowNullValidator (reports VALID if value is null thus suppressing CompareValidator report)

Due to the verbosity of workaround solutions, it would be more convenient to have this option implemented in the library 🙏

Also, please see PR #451 with a similar approach applied to NumberValidator.

To Do

• Check the original issue to confirm it is fully satisfied
• Add solution description to help guide reviewers
• Add unit test to verify new or fixed behaviour
• If apply, add documentation to code properties and package readme