Matrices And Determinants

Let $M$ be a $3 \times 3$ matrix with real entries such that

$$ \left\{\left[\begin{array}{l} x_1 \\ x_2 \\ x_3 \end{array}\right]: M\left[\begin{array}{l} x_1 \\ x_2 \\ x_3 \end{array}\right]=\left[\begin{array}{l} 0 \\ 0 \\ 0 \end{array}\right]\right\}=\left\{\left[\begin{array}{l} x_1 \\ x_2 \\ x_3 \end{array}\right]: x_1+x_2=0=x_2+x_3\right\} $$

What is the value of the determinant of M ?