What does "if not" mean here?

def santa(*says): if not says: return "ho! xmas!" else: return says[0]+"! "+santa(*says[1:])

This is a recursive function with *arg syntax that has troubled my understanding. What does "if not says" mean? Is it equal to "if says == False"? Or "if says is None"? Because if I substitute it with either of both, it gives an error.

How does it link to:

print(santa())

which has no arguments and outputs

"ho! xmas!"

meaning that it satisfies the first conditional statement.