in slf4j-to-log4j-api/src/main/java/org/apache/logging/slf4j/Log4jMarkerFactory.java [69:78]
public Marker getMarker(final Marker marker) {
if (marker == null) {
throw new IllegalArgumentException("Marker must not be null");
}
final Marker m = markerMap.get(marker.getName());
if (m != null) {
return m;
}
return addMarkerIfAbsent(marker.getName(), convertMarker(marker));
}