在SQL中使用TRY CATCH ，抓到错误时，想返回错误号，可是发现却无法获得RETURN的值，提示为NULL，不知道什么原因？？？？？？？？？

------------------------------------SQL-------
ALTER PROCEDURE testingOfReturn
 @Val INT
AS
DECLARE @RESULT INT
SET @RESULT=0
BEGIN TRY
    -- Generate a divide-by-zero error.
    SELECT 1/0;
END TRY
BEGIN CATCH
    --SELECT @RESULT=ERROR_NUMBER();
 --SELECT @RESULT
 RETURN @Val
END CATCH;
--RETURN @RESULT
GO
-------------------------------------------C#

SqlParameter[] para = new System.Data.SqlClient.SqlParameter[2];
        para[0] = new SqlParameter("@Val", SqlDbType.Int);
        para[0].Value = 2;
        para[1] = new SqlParameter("@result", SqlDbType.Int);
        para[1].Direction = ParameterDirection.ReturnValue;
        using (SqlDataReader dr = SqlHelper.ExecuteReader(CommandType.StoredProcedure, "testingOfReturn", para))
        {
            Response.Write(para[1].Value.ToString());
        }

----------------------------------------结果：para[1].Value=null