code: function(feature) {
          var center = feature.geometry.getBounds().getCenterLonLat();
          var cluster = new OpenLayers.Feature.Vector(
              new OpenLayers.Geometry.Point(center.lon, center.lat),
              {count: 1}
          );
          cluster.cluster = [feature];
          return cluster;
      }
docs: Method: createCluster
  Given a feature, create a cluster.
  
  Parameters:
  feature - {<OpenLayers.Feature.Vector>}
  
  Returns:
  {<OpenLayers.Feature.Vector>} A cluster.