[PHP] check null value

[[EMAIL PROTECTED]]

If I have one input text box that when it is submitted to next page, I want to check 
first if it is nothing, then write "na" on next page, else just echo whatever it is, 
is it correct to do this?

if ($fieldname == ""){
$fieldname ="na";
}
...
(then come to the html bit below)
<td><?php echo $fieldname ?></td>

I wonder specificly about the check if it is null part if it is corerct. Any thoughts?
Jack
[EMAIL PROTECTED]
"There is nothing more rewarding than reaching the goal you set for yourself"