Conditional statement with raise on else not working?

 def makeCommand(self, user, host, filepath, filteruser, sudo=None):    
    if sudo is None:
        ["cat", "{filepath}".format(filepath=filepath)]
    elif sudo.lower() == 'yes':
       command = ["sudo", "cat","{filepath}".format(filepath=filepath)]
    elif sudo.lower() == 'no':
       command = ["cat", "{filepath}".format(filepath=filepath)]
    else:
       raise Exception("Please set sudo to either yes/no")

the condition to check 'yes' and 'no' are working well. When the sudo value comes empty I am setting it None as default. The default value is being passed as desired to check if the None condition is working or not I added a print statement and verified but the else part is also running and throwing an exceptions. Why is it so ?

Why is the else part exception running when None is detected