Yes, it's possible. But is is a real security risk and never -ever- recommended. Are you really sure you can not define a password?

This is how you do it:

1.) In the GUI don't enter a password and clear the checkbox "enforce password policy".

or

2.) With T-SQL: CREATE LOGIN [login_name] WITH PASSWORD=N'', DEFAULT_DATABASE=[database_name], CHECK_EXPIRATION=OFF, CHECK_POLICY=OFF