  We show that certain vertex algebras without vacuum vector may be embedded
into vertex algebras. The result is a partial analogue of the simple classical
fact that any rng can be embedded into a ring. A one-line proof of the case of
a vacuum-free vertex algebra (whose vertex operator map is by definition
injective) appeared in Robinson (2010) using a powerful result from the
representation theory of vertex algebras as algebras of mutually local weak
vertex operators. Here we present a more elementary proof of a somewhat more
general case. We also show that our constructions are canonical.
