The sum of solutions of the equation $\frac { \cos x } { 1 + \sin x } = | \tan 2 x | , x \in \left( - \frac { \pi } { 2 } , \frac { \pi } { 2 } \right) - \left\{ - \frac { \pi } { 4 } , \frac { \pi } { 4 } \right\}$