Array bug with additionalItems and empty items

Prerequisites

• I have searched the existing issues
• I understand that providing a SSCCE example is tremendously useful to the maintainers.
• I have read the documentation
• Ideally, I'm providing a sample JSFiddle, Codesandbox.io or preferably a shared playground link demonstrating the issue.

What theme are you using?

core

Version

5.x

Current Behavior

The additionalItems keyword allows one to provide a fixed-length array but allow the user the ability to add on to the end of it. However, this does not work if the fixed-length array is empty. Instead, the form appears to render but the "+" button to add additional items to the array does not work.

Broken Example with Empty Items

The behavior of the additionalItems array should look almost identical (apart from a little extra spacing) to the case where the fixed-length array has one null element with no other information to render: Working Example with One Item

Of course, there is a workaround, which is to move the array item definition in additionalItems into items, since we are no longer really making use of that fixed-length array when it is empty. It would still be preferable if this worked as expected, especially when working with fixed-length arrays of varying lengths -- having to specially handle the case of an array of length 0 adds unnecessary additional complexity.