How to sum with null valued columns in SQL Server

How to SUM NULL valued column in SQL Server :

Here i want to sum columns which contains null values also.
for this we use ISNULL method in SQL Server.
ISNULL required to parameters one is column name,second is value.

Syntax : ISNULL(column,0) .
here i check if column is 'null' then replace it with '0',you can replace null value with any other integer value (you can use string values when you concatenation  tow strings)

Ex:
SELECT SUM(ISNULL(clm1,0)+ISNULL(clm2,0)+ISNULL(clm3,0)) from table1.