[MC-270922] Upgrading a world with a text whose hover event is set to show empty item stack logs error

When upgrading a world contains a text (such as custom stack name, book, etc) with hoverEvent set to show_item an empty item stack, an error is logged.

Steps to Reproduce

Run the following command in 1.20.4

/give @s stick{display:{Name:'{"type":"text","text":"Air","hoverEvent":{"action":"show_item","contents":{"id":"air"}}}'}}

Upgrade the world to 1.20.5-rc1

Expected Result
No error is logged.

Actual Result
An error is logged:

[22:28:07] [Server thread/ERROR]: Tried to load invalid item: 'No key value in MapLike[{"action":"show_item","contents":{"id":"air"}}]; Not a string: {"id":"air"}; Item must not be minecraft:air; Not a json array: {"type":"text","text":"Air","hoverEvent":{"action":"show_item","contents":{"id":"air"}}}; Not a string: {"type":"text","text":"Air","hoverEvent":{"action":"show_item","contents":{"id":"air"}}} missed input: {"minecraft:custom_name":'{"type":"text","text":"Air","hoverEvent":{"action":"show_item","contents":{"id":"air"}}}'}'