Null-density conjecture for finitely generated proper subgroupoids of the cyclic free groupoid

Let $\mathbb{M}$ be the cyclic free groupoid, and let $N$ be a finitely generated proper subgroupoid of $\mathbb{M}$. Null-density conjecture. The subgroupoid $N$ has null density. This conjecture asserts that every finitely generated proper subgroupoid is negligible with respect to the density considered in the paper; the supplied material does not indicate whether the conjecture has been resolved.