Find max+min of m such as equation

Find the range of $m$ satisfying the equation $(m+2) \sin x - 2m \cos x = 2m + 2$ have the solution (in $x$ ) of $\left[ - \dfrac\pi2 , 0 \right ]$ .

If this range can be expressed as $[a,b]$ , submit your answer as $a + b$ .