why blank input print if statement in python

s1 = input("enter 1st string: ")
s2 = input("enter 2nd string: ")

if s2 in s1:
    print("found")
else:
    print("not found")

in the above program if i give "anything" input to s1 and give blank input to s2 it output it print if statement. I want to ask why it is happing?