docs: protected static String join(final Collection<String> elements, final String joinSeparator) {
          String separator = ",";
          if (elements == null) {
              return null;
          }
          if (joinSeparator != null) {
              separator = joinSeparator;
          }
          StringBuilder buffer = new StringBuilder();
          boolean isFirst = true;
          for (String element : elements) {
              if (!isFirst) {
                  buffer.append(separator);
              } else {
                  isFirst = false;
              }
  
              if (element != null) {
                  buffer.append(element);
              }
          }
  
          return buffer.toString();
      }