CRM : OrganizationWebProxyClient is null

string connectionString = "Url=xxxxxxxxxxxxx.crm.dynamics.com; Username=xxxxxxxxxxxx; Password=xxxxxxxxxxxxxxxxx; authtype=Office365";
CrmServiceClient conn = new CrmServiceClient(connectionString);
IOrganizationService _orgService = (IOrganizationService)conn.OrganizationWebProxyClient != null ? (IOrganizationService)conn.OrganizationWebProxyClient : (IOrganizationService)conn.OrganizationServiceProxy;