The order of a null matrix is :

a null matrix → came be of any order

eg:   $\left[\begin{array}{ll}0 & 0 \\ 0 & 0\end{array}\right]_{2 \times 2}$

$\left[\begin{array}{l}0 \\ 0 \\ 0\end{array}\right]_{3 \times 1}$

$\left[\begin{array}{lll}0 & 0 & 0\end{array}\right]_{1 \times 3}$