code: public static ArrayList<ConfigSource> getDefaultSources(ClassLoader classloader) {
          ArrayList<ConfigSource> sources = new ArrayList<>();
  
          sources.add(new SystemConfigSource());
          sources.add(new EnvConfigSource());
  
          sources.addAll(getPropertiesFileConfigSources(classloader));
  
          return sources;
      }
docs: The classloader's loadResources method is used to locate resources of
  name {#link ConfigConstants.CONFIG_PROPERTIES} as well as process environment
  variables and Java System.properties
  
  @param classloader
  @return the default sources found