docs: private static String toJsonCollection(Collection objects) {
          Iterator iterator = objects.iterator();
          if (!iterator.hasNext()) {
              return "";
          }
          final Object first = iterator.next();
          if (!iterator.hasNext()) {
              return toJson(first);
          }
  
          final StringBuilder buf = new StringBuilder();
          if (first != null) {
              buf.append(toJson(first));
          }
  
          while (iterator.hasNext()) {
              buf.append(',');
              final Object obj = iterator.next();
              if (obj != null) {
                  buf.append(toJson(obj));
              }
          }
          return buf.toString();
      }