Grothendieck ring of finite dimensional modules over quantum affine algebras

Question

Let $\mathcal{C}$ be the category of all finite dimensional modules over $U_q(\hat{g})$, where $g$ is a simple Lie algebra over $\mathbb{C}$. Let $M$ be a module in $\mathcal{C}$. Suppose that $M$ has a composition series $0=M_0 \subset M_1 \subset \cdots \subset M_n = M$. Do we have $[M]=\sum_{i=1}^n [M_i/M_{i-1}]$ in the Grothendieck ring of $\mathcal{C}$?