If Profile Field Empty

[TheInsaneManiac]

I want to make a script not run if a profile field is empty, but can't seem to find a conditional for this. I don't want this script to run if my profile field is not filled in:

if($vbulletin->options['xbl_avatar_system_enable_product'] AND $vbulletin->options['xbl_avatar_system_display_navbar'])
{
$xblavatarfield = $vbulletin->options['xbl_avatar_system_userfield'];
eval('$xblavatarhead = "<td style=\"padding:1px\"><a href=\"member.php?".$vbulletin->session->vars[sessionurl]."u=".$vbulletin->userinfo[userid]."\"><img src=\"http://avatar.xboxlive.com/avatar/".$vbulletin->userinfo[$xblavatarfield]."/avatarpic-l.png\" border=\"0\" /></a></td>";');
}