input: Write a function to sort a given list of names alphabetically. If the given list is empty then return an empty list.
  
  def sort_names(names):
      if not names:
          return []
      names.sort()
      return names
  
  assert sort_names(["John", "Harry", "Robert"])==['Harry', 'John', 'Robert']
  assert sort_names(["Alice", "Bob", "Charlie"])==['Alice', 'Bob', 'Charlie']
  assert sort_names(["Zack", "Yvonne", "Xavier"])==['Xavier', 'Yvonne', 'Zack']
  assert sort_names([])==[]
  assert sort_names(["Adam"])==['Adam']
output: def sort_names(names):
      if not names:
          return []
      names.sort()
      return names