input: Write a function to find the most common fruit (case-sensitive) in a given list of strings. The function should return the fruit name as a string. If the list is empty, the function should return None.
  assert most_common_fruit(['Apple', 'Orange', 'Apple', 'Pineapple', 'Grape', 'Apple'])=='Apple'
  assert most_common_fruit(['Apple', 'Orange', 'Apple', 'Pineapple', 'Grape'])=='Apple'
  assert most_common_fruit(['Orange', 'Pineapple', 'Grape'])=='Orange'
  assert most_common_fruit(['Apple', 'Apple', 'Apple'])=='Apple'
  assert most_common_fruit([])==None
output: def most_common_fruit(fruits):
      if not fruits:
          return None
      fruit_count = {}
      for fruit in fruits:
          if fruit in fruit_count:
              fruit_count[fruit] += 1
          else:
              fruit_count[fruit] = 1
      return max(fruit_count, key=fruit_count.get)