UnityWebRequest Cannot create error on 5.4.0b1

Unity Engine
1

Hello! After start WebGL build 5.4.0b1 on Chrome or Firefox bouth I have this erros:

Cannot create web request without initializing the system
UnityEngine.Networking.UnityWebRequest:.ctor(String)

Unable to initialize UnityWebRequest
UnityEngine.Networking.UnityWebRequest:.ctor(String)

System.NullReferenceException: UnityWebRequest has already been destroyed
at UnityEngine.Networking.UnityWebRequest.InternalSetUrl (System.String url)
at UnityEngine.Networking.UnityWebRequest.set_url (System.String value)
at UnityEngine.Networking.UnityWebRequest…ctor (System.String url)

2

Solved

//initializing first
var request = new UnityWebRequest();
//then set url
request.url = "url";