m_InstanceID != 0 when downloading texture from the server

I'm getting this error when trying to download the texture from the server.

Here is the code (link works):

         UnityWebRequest www = UnityWebRequest.GetTexture("https://0.gravatar.com/avatar/fc2beef90fad49f83d79650a10b5c030?s=256&d=identicon&r=G");
         www.SetRequestHeader("Accept", "image/*");
         async = www.Send();
         while (!async.isDone)
             yield return null;

         if (www.isError) {
             Debug.Log(www.error);
         } else {
             tex = DownloadHandlerTexture.GetContent(www);    // <-------------------
         }

The error looks like this:

 m_InstanceID != 0
 UnityEngine.Networking.DownloadHandlerTexture:GetContent(UnityWebRequest)