input: Write a function to create a Flask API that takes a list or array of integers and returns their minimum and maximum values. If the list is empty, return a message indicating that the list is empty.
  assert minmax([12, 4, 9, 24, -5])=={'min': -5, 'max': 24}
  assert minmax([])=='The list is empty.'
  assert minmax([0])=={'min': 0, 'max': 0}
  assert minmax([-10, -10, -10])=={'min': -10, 'max': -10}
  assert minmax([3, 3, 4, 3])=={'min': 3, 'max': 4}
output: def minmax(lst):
      if not lst:
          return 'The list is empty.'
      return {'min': min(lst), 'max': max(lst)}