code: private String getCategory(String group)
      {
          for (final PathCategory category : categories.values())
          {
              if (category.getGroups().contains(group))
              {
                  return category.getName();
              }
          }
          return null;
      }
docs: Get the group category.
  
  @param group The group name.
  @return The category name (<code>null</code> if undefined).