  In this paper, we show that the $L^2$-optimal condition implies the
$L^2$-divisibility of $L^2$-integrable holomorphic functions. As an
application, we offer a new characterization of bounded $L^2$-domains of
holomorphy with null thin complements using the $L^2$-optimal condition, which
appears to be advantageous in addressing a problem proposed by Deng-Ning-Wang.
Through this characterization, we show that a domain in a Stein manifold with a
null thin complement, admitting an exhaustion of complete K\"ahler domains,
remains Stein. By the way, we construct an $L^2$-optimal domain that does not
admit any complete K\"ahler metric.
