docs: public List<ImageConfiguration> resolve(ImageConfiguration unresolvedConfig, MavenProject project, MavenSession session) {
          injectExternalConfigActivation(unresolvedConfig, project);
          Map<String,String> externalConfig = unresolvedConfig.getExternalConfig();
          if (externalConfig != null) {
              String type = externalConfig.get("type");
              if (type == null) {
                  throw new IllegalArgumentException(unresolvedConfig.getDescription() + ": No config type given");
              }
              ExternalConfigHandler handler = registry.get(type);
              if (handler == null) {
                  throw new IllegalArgumentException(unresolvedConfig.getDescription() + ": No handler for type " + type + " given");
              }
              return handler.resolve(unresolvedConfig, project, session);
          } else {
              return Collections.singletonList(unresolvedConfig);
          }
      }