input: Write a function to debug the provided Python code which consists of two functions f1 and f2. The first function f1 takes a parameter x and should return x + 1 instead of performing the operation without a return statement. The second function f2 takes a parameter x and should return the square of the result of f1(x). Ensure that the corrected code is defined and provides the correct output when f2 is called with the value 2.
  def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)
  
  print(f2(2)) #Output: 9
  assert f2(2)==9
  assert f2(3)==16
  assert f2(0)==1
  assert f2(-1)==0
  assert f2(-2)==1
output: def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)