Filter "has_equipment" cannot test for an empty string ("") or air

The bug

When attempting to test for empty equipment using the "has_equipment" filter, the IDs "air" and an empty string ("") both fail. This leaves no way to test if the hand is empty through filters, short of negating a filter testing every single item in the game.

Steps to reproduce:

The supplied behavior pack modifies the player's behavior to include an additional trigger; it tests to see if the player is sneaking, and if they are either holding air or an empty string ("").

• Create a new world with Holiday Creator Features enabled (or use an existing one).
• Install the attached behavior pack and apply it to a world.
• Once in the world, sneak with an empty hand. This should meet all the conditions for an event to trigger a command.
• Observe chat for a success message.

→ Nothing occurs. The filter looking for air and looking for an empty string could not succeed.