docs: private PerMessageCompressionExtension findAgreedPerMessageCompressionExtension()
      {
          if (mAgreedExtensions == null)
          {
              return null;
          }
  
          for (WebSocketExtension extension : mAgreedExtensions)
          {
              if (extension instanceof PerMessageCompressionExtension)
              {
                  return (PerMessageCompressionExtension)extension;
              }
          }
  
          return null;
      }