code: public Class<? extends LoggerContextFactory> loadLoggerContextFactory() {
          if (loggerContextFactoryClass != null) {
              return loggerContextFactoryClass;
          }
          if (className == null) {
              return null;
          }
          final ClassLoader loader = classLoader.get();
          if (loader == null) {
              return null;
          }
          try {
              final Class<?> clazz = loader.loadClass(className);
              if (LoggerContextFactory.class.isAssignableFrom(clazz)) {
                  return clazz.asSubclass(LoggerContextFactory.class);
              }
          } catch (final Exception e) {
              LOGGER.error("Unable to create class {} specified in {}", className, url.toString(), e);
          }
          return null;
      }
docs: Loads the {@link org.apache.logging.log4j.spi.LoggerContextFactory} class specified by this Provider.
  
  @return the LoggerContextFactory implementation class or {@code null} if there was an error loading it