There are three ways to replace the NULL value with default values
1) You can use ISNULL function to replace Null with No manager
Select ISNULL(NULL,'No manager')
2) You can use the COAlESCE function
Select CoalEscE(NULL,'No manager' )
3) Case statement
select Case when Name is null then 'No manager' else Name end
from Employee
You can see also ISNULL (Transact-SQL)