7 . In $\triangle \mathbf{A B C}$, the sides opposite to angles $\mathbf{A} 、 \mathbf{B} 、 \mathbf{C}$ are $a 、 \mathbf{b} 、 \mathbf{c}$ respectively. If $a^{2}+b^{2}=2019 c^{2}$, then $\frac{\cot C}{\cot A+\cot B}=$