input: Write a function most_common_fruit(fruit_list) that takes a list containing fruit names and returns the most common fruit name. If there are multiple fruits with the same highest frequency, return the first one encountered.
  
  assert most_common_fruit(['Apple', 'Orange', 'Apple', 'Pineapple', 'Grape', 'Apple'])=='Apple'
  assert most_common_fruit(['Banana', 'Banana', 'Apple', 'Apple', 'Banana'])=='Banana'
  assert most_common_fruit(['Strawberry', 'Blueberry', 'Blueberry'])=='Blueberry'
  assert most_common_fruit(['Orange'])=='Orange'
  assert most_common_fruit([])==None
output: def most_common_fruit(fruit_list):
      if not fruit_list:
          return None
      fruit_count = {}
      for fruit in fruit_list:
          if fruit in fruit_count:
              fruit_count[fruit] += 1
          else:
              fruit_count[fruit] = 1
      most_common = max(fruit_count, key=fruit_count.get)
      return most_common