input: Write a function to add two numbers together and print the result. If the input numbers are not provided, the function should not print anything.
  def add(a=None, b=None):
      if a is not None and b is not None:
          sum = a + b
          print(sum)
  
  add(5,7)
  add(3,4)
  add(10,20)
  add(0,0)
  add(0,None)
  add(None,None)
  add()
  assert add(5,7)==None
  assert add(3,4)==None
  assert add(10,20)==None
  assert add(0,0)==None
  assert add(0,None)==None
  assert add(None,None)==None
  assert add()==None
output: def add(a=None, b=None):
      if a is not None and b is not None:
          sum = a + b
          print(sum)