input: Write a function to debug the provided Python code. The function should correct any logical or syntactical errors in the provided code and ensure it produces the expected output. The provided code consists of two functions, `f1` and `f2`, where `f1` is a function that takes an argument `x` and should increment `x` by 1, while `f2` is a function that takes an argument `x`, calls `f1` twice with `x` as the argument, and then returns the square of the result of `f1`. The corrected code should be tested with the input `2` and should output `9`. If the input code is empty or contains only irrelevant content, return the input as is.
  def debug_code(code_input):
      if not code_input or "def" not in code_input:
          return code_input
      
      code_input = code_input.replace("y = x + 1", "return x + 1")
      return code_input
  
  assert debug_code("""
  def f1 (x):
   y = x + 1
  def f2(x):
   return f1(x)*f1(x)
  
  f2(2)
  """) == """
  # define f1 #
  def f1(x):
      return x + 1
  
  # define f2 #
  def f2(x):
      return f1(x) * f1(x)
  
  # call f2 #
  print(f2(2)) #Output: 9
  """
  assert debug_code("") == ""
  assert debug_code("This is not code") == "This is not code"
output: def debug_code(code_input):
      if not code_input or "def" not in code_input:
          return code_input
      
      code_input = code_input.replace(" y = x + 1", "    return x + 1")
      code_input = code_input.replace("return f1(x)*f1(x)", "return f1(f1(x))")
      return code_input