code: public static String collectionToDelimitedString(@Nullable final Collection<?> coll,
        final String delim) {
      return StringUtils.collectionToDelimitedString(coll, delim, "", "");
    }
docs: Convert a {@code Collection} into a delimited {@code String} (e.g. CSV).
  <p>
  Useful for {@code toString()} implementations.
  
  @param coll the {@code Collection} to convert
  @param delim the delimiter to use (typically a ",")
  @return the delimited {@code String}