check for callback handler validity before calling on unit action buttons
check for callback handler validity before calling on unit action buttons
CanonicalJS/juju-gui,mitechie/juju-gui,jrwren/juju-gui,jrwren/juju-gui,bac/juju-gui,mitechie/juju-gui,bac/juju-gui,CanonicalJS/juju-gui,mitechie/juju-gui,jrwren/juju-gui,bac/juju-gui,jrwren/juju-gui,mitechie/juju-gui,bac/juju-gui,CanonicalJS/juju-gui