Your task is to write a function sig$\_$power according to the following specifications:

Your function takes as it's input a sampled signal named $$

this signal is passed as a NumPy array

the signal may be complex$-$valued, e$.$g$.,$ a complex exponential signal

your function must compute and return the average power of the signal.

Note that power is always real$-$valued, even if $$ is complex

The power $P$ of the discrete$-$time signal with samples $x[n],n=0,1,$dots,$N-1$ is computed as

$P=\frac{1}{N}{\displaystyle \underset{n=0}{\overset{N-1}{}}}|x[n]{|}^2.$

Your function must handle the special case that $$ ontains no samples, i$.$e$.,N=0.$ In that case, your function must return the special Python value None.

don't return the string 'None' ; the constant None is a special value in Python

Your function must include a proper doc string.