code: public static String stringifyPrompts(Prompt[] prompts)
      {
          if (prompts == null)
          {
              return null;
          }
  
          String[] array = new String[prompts.length];
  
          for (int i = 0; i < prompts.length; ++i)
          {
              array[i] = (prompts[i] == null) ? null : prompts[i].name().toLowerCase();
          }
  
          return join(array, " ");
      }
docs: Stringify an array of {@link Prompt}.
  
  @param prompts
  An array of {@link Prompt}. If {@code null} is given,
  {@code null} is returned.
  
  @return
  A string containing lower-case prompt names using
  white spaces as the delimiter.
  
  @since 2.5