How to Write Case statements in sql view

CREATE view [dbo].[vwcall_master]
as
select
case when Call_Duration is null then 'Enter duration' else Call_Duration end as Call_Duration,
case when Call_To_NumberExtn is null then '00000000' else Call_To_NumberExtn end as Call_To_NumberExtn,
case when Client_Id is null then '0' else Client_Id end as Client_Id,
case when Client_Name is null then ' Enter Clientname' else Client_Name end as Client_Name,

Call_Id,
User_Id,
Call_From_UserName,
Call_From_NumberExtn,
Call_DateTime,
UpLoade_Audio_Call,
Rating,
Rating_UserId
from call_master