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 files and directories in that directory. If the directory path is not provided, the function should list the contents of the current directory.
  assert list_directory_contents("path/to/directory")==["file1.txt", "file2.txt", "folder1"]
  assert list_directory_contents("nonexistent/path")==[]
  assert list_directory_contents("")==["current_file.txt", "subfolder"]
output: import os
  
  def list_directory_contents(path='.'):
      if not os.path.exists(path):
          return []
      return os.listdir(path)