In base $-2$ notation, digits are $0$ and $1$ only and the places go up in powers of $-2$. For example, $11011$ stands for ${\left(-2\right)}^4+{\left(-2\right)}^3+{\left(-2\right)}^1+{\left(-2\right)}^0$ and equals number $7$ in base $10$. If the decimal number $2019$ is expressed in base $-2$, how many non-zero digits does it contain?