Function is_bare_varint 

fn is_bare_varint(key: u64) -> bool

Whether a Table 7 parameter’s value is a bare varint.

FILL_TIMEOUT (0x0A, Section 9.19.5) is the only one. LOCATION_FILTER (0x21) also opens with a varint, but a varint alone is only its type, and accepting one here would write a bare 0x05 as Next Object and a bare 0x00 as no filter: the codec’s own encoder refuses that value, so this one does too.