input: Write a function to list the contents of a directory. The function should take the directory path as an input and return a list of filenames in that directory. If the directory does not exist, the function should return an empty list.
  assert get_directory_contents("/path/to/existing/directory")==['file1.txt', 'file2.txt', 'subdir']
  assert get_directory_contents("/path/to/non/existent/directory")==[]
  assert get_directory_contents(".")==['current_directory_contents_list']
output: def get_directory_contents(directory_path):
      import os
      if not os.path.exists(directory_path):
          return []
      return os.listdir(directory_path)