function clusterCircleStyle(cluster, resolution) {
  if (cluster !== clickFeature || resolution !== clickResolution) {
    return null;
  }
  const clusterMembers = cluster.get('features');
  const centerCoordinates = cluster.getGeometry().getCoordinates();
  return generatePointsCircle(
    clusterMembers.length,
    cluster.getGeometry().getCoordinates(),
    resolution,
  ).reduce((styles, coordinates, i) => {
    const point = new Point(coordinates);
    const line = new LineString([centerCoordinates, coordinates]);
    styles.unshift(
      new Style({
        geometry: line,
        stroke: convexHullStroke,
      }),
    );
    styles.push(
      clusterMemberStyle(
        new Feature({
          ...clusterMembers[i].getProperties(),
          geometry: point,
        }),
      ),
    );
    return styles;
  }, []);
}
Style for clusters with features that are too close to each other, activated on click.
@param {Feature} cluster A cluster with overlapping members.
@param {number} resolution The current view resolution.
@return {Array<Style>|null} A style to render an expanded view of the cluster members.