The bug
Commands which use ids (e.g. block, entity or item ids) show incomplete error messages when the id is malformed, i.e. is not a valid resource location consisting of [a-z0-9/._-]
:
/give @s does_not_exist
✔ "Unknown item 'minecraft:does_not_exist'"
/give @s Does_not_exist
❌ "Unknown item 'minecraft:'"
The entered id is not contained in the error message
How to reproduce
/give @s Does_not_exist
/setblock ~ ~ ~ Does_not_exist
/summon Does_not_exist
Can confirm in 20w49a.