code: public static String toDelimitedString(Collection<?> list, String delim) {
          if (list == null || list.isEmpty()) {
              return EMPTY;
          }
          StringBuilder sb = new StringBuilder();
          boolean first = true;
          for (Object o : list) {
              if (!first) {
                  sb.append(delim);
              }
              sb.append(o);
              first = false;
          }
          return sb.toString();
      }
docs: Convert a {@code Collection} into a delimited {@code String} (e.g. CSV).
  <p>Useful for {@code toString()} implementations.
  
  @param list the collection
  @param delim the delimiter to use (typically a ",")
  @return the delimited {@code String}