'addMarker' using address fails

[d-danger]

While this works perfectly:

$('#map').gMap({
    maptype: 'ROADMAP',
    zoom: 10,
    latitude: 51.51,
    longitude: -0.05,
    markers: [{
        address: 'London'
    }]
});

this doesn't work:

$('#map').gMap({
    maptype: 'ROADMAP',
    zoom: 10,
    latitude: 51.51,
    longitude: -0.05
});

$('#map').gMap('addMarker',{
    address: 'London'
});