default List<OsmRelationInfo> preprocessOsmRelation(OsmElement.Relation relation) {
    return null;
  }
Extracts information from <a href="https://wiki.openstreetmap.org/wiki/Relation">OSM relations</a> that will be
passed along to {@link #processFeature(SourceFeature, FeatureCollector)} for any OSM element in that relation.
<p>
The result of this method is stored in memory.
<p>
The default implementation returns {@code null} to ignore all relations

@param relation the OSM relation
@return a list of relation info instances with information extracted from the relation to pass to
        {@link #processFeature(SourceFeature, FeatureCollector)}, or {@code null} to ignore.
planetiler-core/src/main/java/com/onthegomap/planetiler/Profile.java