Why is this the output I am getting?

[wlsa]

def func_a():
    print('inside func_a')
def func_c(z):
    print('inside func_c')
    return z()
print(func_c(func_a))

the output I get is
inside func_c
inside func_a
None

I'm having a hard time understanding how putting a function as an input into another function gives me this output.