input: Write a function to list the contents of a given directory. The function should take a directory path as input and return a list of its contents. Use the os module to achieve this. If the directory does not exist or is empty, the function should return an empty list.
  assert list_directory_contents("/path/to/existing_directory")==['file1.txt', 'file2.txt', 'directory']
  assert list_directory_contents("/path/to/nonexistent_directory")==[]
  assert list_directory_contents("/path/to/empty_directory")==[]
output: def list_directory_contents(directory_path):
      import os
      if not os.path.exists(directory_path):
          return []
      return os.listdir(directory_path)