code: @Nullable
    public static Resource mergeResources(List<Resource> resources) {
      Resource currentResource = null;
      for (Resource resource : resources) {
        currentResource = merge(currentResource, resource);
      }
      return currentResource;
    }
docs: Returns a {@link Resource} that runs all input resources sequentially and merges their results.
  In case a type of label key is already set, the first set value takes precedence.
  
  @param resources a list of resources.
  @return a {@code Resource}.
  @since 0.18