Solution (source code)

= Solution

The reduced equations are $x+z=0$ and $y+2z=0$. Thus the <null space> is the line
$$
\boxed{\ker A=\left\{t\begin{pmatrix}-1\\-2\\1\end{pmatrix}:t\in\mathbb R\right\}.}
$$
The nonzero spanning vector gives a one-element <basis>, so the <nullity> is one.