Why is the click add_command not working?

Running the following code as python script.py does nothing,I expect at least the click.echo statement to get printed, sounds like the call to first_command doesn't work, any idea why?

import click

def multiple_input_option(**option_kwargs):
    def decorator(func):
        def _callback(ctx, param, value):
            ctx.obj['multiple_options'] = value

        help_text = 'some options to get from user'

        keyword_arguments = {
            'help': help_text,
            'callback': _callback,
            'expose_value': False,
            'multiple': True,
        }
        keyword_arguments.update(**option_kwargs)

        return click.option('--multiple-options', '-e', **keyword_arguments)(func)

    return decorator

@click.command()
@multiple_input_option()
def first_command(ctx):
    click.echo('> hello...first_command')
    command_param_data = ctx.obj.keys()

    click.echo(json.dumps(command_param_data, indent=2))

@click.group()
def hello_world(ctx):
    """
    Your plugin description here
    """
    ctx.ensure_object(dict)



# This is how we add more sub-commands
hello_world.add_command(first_command)

from Why is the click add_command not working?