Sql server抛出异常（RAISERROR）

create PROCEDURE [dbo].[spTASKS_ASSIGNED_Update]
    (
      @ID UNIQUEIDENTIFIER OUTPUT ,
      @MODIFIED_USER_ID UNIQUEIDENTIFIER = NULL ,
      @ASSIGNED_USER_ID UNIQUEIDENTIFIER = NULL             
    )
AS
    DECLARE @ASSIGNED_USER_NAME NVARCHAR(100);
    SELECT  @ASSIGNED_USER_NAME = ASSIGNED_TO_NAME
    FROM    dbo.vwTASKS
    WHERE   ID = @ID;
    IF @ASSIGNED_USER_NAME IS NULL
        BEGIN
            UPDATE  [TASKS]
            SET     [MODIFIED_USER_ID] = @MODIFIED_USER_ID ,
                    [DATE_MODIFIED] = GETDATE() ,
                    [ASSIGNED_USER_ID] = @ASSIGNED_USER_ID ,
                    STATUS = 'In progress'
            WHERE   [ID] = @ID;   
        END;
    ELSE
        BEGIN
            RAISERROR    
  
  (N'Submit failed, this task is assigned to %s!',    
  16, -- Severity.    
  1, -- State.  
  @ASSIGNED_USER_NAME
  );      
        END;