code: @SuppressWarnings("unchecked")
      public static <T> Optional<Key<T>> resolveDefaultQualifier(Map<Key<?>, Class<?>> bindings,
              ClassConfiguration<?> classConfiguration, String property, Class<?> qualifiedClass,
              TypeLiteral<T> genericInterface) {
          Key<T> key = null;
  
          if (classConfiguration != null && !classConfiguration.isEmpty()) {
              String qualifierName = classConfiguration.get(property);
              if (qualifierName != null && !"".equals(qualifierName)) {
                  try {
                      ClassLoader classLoader = ClassLoaders.findMostCompleteClassLoader(BusinessUtils.class);
                      Class<?> qualifierClass = classLoader.loadClass(qualifierName);
                      if (Annotation.class.isAssignableFrom(qualifierClass)) {
                          key = Key.get(genericInterface, (Class<? extends Annotation>) qualifierClass);
                      } else {
                          throw BusinessException.createNew(BusinessErrorCode.CLASS_IS_NOT_AN_ANNOTATION)
                                  .put("class", qualifiedClass)
                                  .put("qualifier", qualifierName);
                      }
                  } catch (ClassNotFoundException e) {
                      key = Key.get(genericInterface, Names.named(qualifierName));
                  }
              }
          }
  
          if (key == null || bindings.containsKey(Key.get(key.getTypeLiteral()))) {
              return Optional.empty();
          } else {
              return Optional.of(key);
          }
      }
docs: Returns the Guice key qualified with the default qualifier configured for the specified class.