docs: public static String toExtensionHeader(final List<WebSocketExtension> extensions) {
          StringBuilder extensionsHeader = new StringBuilder();
          if (extensions != null && extensions.size() > 0) {
              Iterator<WebSocketExtension> it = extensions.iterator();
              while (it.hasNext()) {
                  WebSocketExtension extension = it.next();
                  extensionsHeader.append(extension.getName());
                  for (Parameter param : extension.getParameters()) {
                      extensionsHeader.append("; ").append(param.getName());
                      if (param.getValue() != null && param.getValue().length() > 0) {
                          extensionsHeader.append("=").append(param.getValue());
                      }
                  }
                  if (it.hasNext()) {
                      extensionsHeader.append(", ");
                  }
              }
          }
          return extensionsHeader.toString();
      }