I want to use contributions like

route[PROXY_MEDIA]
{
    if (is_method("BYE|CANCEL")) {
        # passing message for RTPengine processing
    } else if (!sdp_content()) {
        return;
    }
    # more instructions here
    ...
    rtpengine_manage();
}

Now Kamailio cannot start because first if block has empty actions.
How does nothing in the actions?
I want to avoid not needed log messages and do not use constructions like

if (!sdp_content() and ! is_method("BYE|CANCEL")) {
    return;
}