/**
* Implementation-internal method for handling an incoming command message.
*
* @param command Command message
* @return Behavior which should be used with the next message. Return null if this actor should shut down.
*/
/**
* Implementation-internal method for handling an incoming command message.
*
* @param command Command message
* @return Behavior which should be used with the next message. Return null if this actor should shut down.
*/