Missing predicates return true/false rather than failing

@a[advancements={does_not_exist=false}]   // finds nobody
@a[advancements={does_not_exist=true}]    // finds nobody
@a[predicate=!does_not_exist]             // finds everyone

/execute unless predicate aklsdjfaksjfa
/execute if entity @s[predicate=!alskdjf]