code: public void toFile(String fileName) {
          Preconditions.checkNotNull(fileName, "File Name cannot be null.");
  
          Config configuration = buildFromFile(fileName);
  
          if (annotationClass == null) {
              binder.bind(configClass).toInstance(configuration);
  
          } else {
              binder.bind(configClass).annotatedWith(annotationClass).toInstance(configuration);
          }
      }
docs: This method will load the configuration using a {@link io.dropwizard.configuration.ConfigurationFactory} to load
  the file from the current relative working directory.
  
  @param fileName The filename to load.