@Override
    public <R> R executeAndQuery(Command<ROOT, R> cmd) {
        return this.executeAndQuery((ContextCommand<ROOT, R>) cmd);
    }
@ Override public < R > R executeAndQuery ( Command < ROOT , R > cmd ) { return this . executeAndQuery ( ( ContextCommand < ROOT , R > ) cmd ) ; }
Perform command on system.
<p>
Inside command can be any code doing any changes. Such changes are
guaranteed to be preserved (if only command ended without exception).

@param cmd