Contains Query on multiple columns

How do I search multiple columns using LINQ to SQL when any one of the column could be null?

IEnumerable<User> users = from user in databaseUsers
        where
             user.ScreenName.Contains(search)
             || user.FirstName.Contains(search)
             || user.LastName.Contains(search)
        select user;

I keep getting this exception:

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and 开发者_StackOverflow中文版where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

add not null condition user.Property != null

  IEnumerable<User> users = from user in databaseUsers
    where
         (user.ScreenName != null && user.ScreenName.Contains(search))
         || (user.FirstName != null && user.FirstName.Contains(search))
         || ( user.LastName != null && user.LastName.Contains(search))
    select user;

IEnumerable<User> users = from user in databaseUsers
where
     (user.ScreenName + ' ' + user.FirstName + ' ' + user.LastName).Contains(search)
select user;

Either your user is a null entry, or your databaseUsers are not initialized.