  We construct a basis of the space ${\text S}_{14}({\text{Sp}}_{12}({\mathbb
Z}))$ of Siegel cusp forms of degree $6$ and weight $14$ consisting of harmonic
theta series. One of these functions has vanishing order $2$ at the boundary
which implies that the Kodaira dimension of $\mathcal{A}_6$ is non-negative.
