SQL In Crystal Reports

I'm new to SQL but have quite happily been using Crystal Reports without it until now.

I am creating a letter template and it has the name at the top then the address

<name>

<address1>
<address2>
<address3>
<address4>

There is always an address 1, but maybe not a 3 or a 4, and aparently we dont want any line gaps to show, so I figured i should use an isnull to eliminate the line and to move the other address line up?

Not sure what to put though, any ideas?

Thanks in advance for any help :o)