Guardian beam is not rendered if targeted entity has ID 0, as it does not use the OptionalInt metadata type

The bug

The guardian beam is not rendered if the attacked entity has the entity id 0.  Guardians directly write the entity ID in an integer metadata field, and assume 0 means no target (unlike fireworks, which use an OptionalInt (MC-111480) to prevent this).

 

Since entity IDs start at 1 after 19w05a, this is unlikely to cause problems in practice, but it is still weird that one entity uses OptionalInt and the other doesn't.