How do you start/ stop streams playing in the karaf console/ rules?

In the karaf console I can start a stream playing but I can’t find anyway to stop it! I found something in eclipse about setting the stream to null but I can’t work out how to do it from the karaf console.

Also how do you start/stop a stream playing within a rule and specify the sink? This doesn’t seem to be in the documentation https://github.com/openhab/openhab1-addons/wiki/Actions#audio-actions

example
openhab> audio stream enhancedjavasound “http://bbcmedia.ic.llnwd.net/stream/bbcmedia_radio2_mf_p

openhab> audio stream enhancedjavasound ""
> URL not valid

openhab> audio stream enhancedjavasound null
> Error executing command: java.lang.NullPointerException

openhab> audio stream enhancedjavasound NULL
> URL not valid