input: Write a function to sort an array in ascending order. The function should return the sorted array. If the input array is empty, the function should return an empty array.
  
  ### Function:
  
  
  def sort_ascending(array):
      if not array:
          return []
      array.sort()
      return array
  
  
  ### Test Cases:
  
  assert sort_ascending([10, 3, 9, 1, 15, 2]) == [1, 2, 3, 9, 10, 15]
  assert sort_ascending([7, 5, 8, 4, 1]) == [1, 4, 5, 7, 8]
  assert sort_ascending([]) == []
  assert sort_ascending([3, 3, 3, 3]) == [3, 3, 3, 3]
output: def sort_ascending(array):
      if not array:
          return []
      array.sort()
      return array