input: Write a python function to get the first key from a dictionary.
  assert get_first_key({'a': 1, 'b': 2, 'c': 3}) == 'a'
  assert get_first_key({}) == None
  assert get_first_key({'x': 9, 'y': 8}) == 'x'
output: def get_first_key(d):
      if d:
          return next(iter(d))
      return None