code: public <E extends Enum<E>> E optEnum(Class<E> clazz, int index) {
          return this.optEnum(clazz, index, null);
      }
docs: Get the enum value associated with a key.
  
  @param <E>
  Enum Type
  @param clazz
  The type of enum to retrieve.
  @param index
  The index must be between 0 and length() - 1.
  @return The enum value at the index location or null if not found