input: Write a function to list the contents of a directory. If the directory is empty, it should return an empty list.
  assert list_directory_contents(directory_path="test_directory")==['file1.txt', 'file2.txt', 'subdir']
  assert list_directory_contents(directory_path="empty_directory")==[]
  assert list_directory_contents(directory_path="non_existent_directory")==None
output: def list_directory_contents(directory_path):
      import os
      if not os.path.exists(directory_path):
          return None
      return os.listdir(directory_path)