public String toJoinedString(final String separator) {
        final StringBuilder sb = new StringBuilder();
        boolean first = true;
        for (Object element : getCollectionForRead()) {
            if (!first && separator != null) {
                sb.append(separator);
            }
            first = false;
            sb.append(element);
        }
        return sb.toString();
    }
mimics {@link java.util.stream.Collectors#joining(CharSequence)}
main/src/main/java/cgeo/geocaching/utils/CollectionStream.java