input: Write a function that takes two large numbers represented as strings and returns their sum as a string, ensuring that the function handles large numbers efficiently.
  assert add_large_numbers("111", "1337")=="1448"
  assert add_large_numbers("5000", "6000")=="11000"
  assert add_large_numbers("123456789", "987654321")=="1111111110"
  assert add_large_numbers("999", "1")=="1000"
  assert add_large_numbers("", "")=="0"
output: def add_large_numbers(num1, num2):
      if not num1:
          num1 = "0"
      if not num2:
          num2 = "0"
      return str(int(num1) + int(num2))