Can all pass filers have a pole/zero at the origin of the root locus

I came across this root locus diagram in my DSP class. It has a pole at the origin, another pole within the unit circle and a zero just outside the unit circle. I understand that the poles and zeros should be complex conjugates for an all pass filter. So will a pole or a zero at the origin prevent the system from being an all pass?My professor tells me that the pole at the origin is allowed. So that is basically leaving me confused.Can anyone explain how this is possible?

$$H(z) = z^{-1} = \frac{1}{z} = \frac{1}{z-0}$$
which means there is a pole at $z=0$. and it is true that $\left|H\left( e^{j \omega} \right)\right| = 1$, so it's an APF.