input: Write a function to improve the provided function by using Python built-in functions. The provided function takes in an array of numbers and returns the sum of all the numbers. After improvement, the function should utilize the built-in sum function. If the array is empty, the function should return 0.
  
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)
  
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([10, 20, 30])==60
  assert sum_array([-1, -2, -3])==-6
  assert sum_array([])==0
  assert sum_array([0])==0
output: def sum_array(array):
      return sum(array)