It says s is null on line 37

here's the code I have...
Code:
// JavaScript Document
selectIDs=['companyName','sloganS','nameS','titleS','address1S','address2S','phoneS','cellS','emailS','websiteS'];
function attachBehaviors() { 
 // Attach event handler to your select objects  
   for (i=0 ; i<selectIDs.length ; i++){
    var s = document.getElementById("select_"+selectIDs[i]);  
    if( s ) {  
      s.onchange = function(){selectCallback(s,selectIDs[i]);};  
    }
   }
}
fontData=[];
fontData[443]='Arial';
fontData[444]='Book Antiqua Italic';
fontData[445]='Bradley Hand ITC';
fontData[446]='Century Gothic';
fontData[447]='Comic Sans MS';
fontData[448]='Copperplate Gothic Bold';
fontData[449]='Courier';
fontData[461]='edwardian script ITC';
fontData[462]='Garamond';
fontData[463]='Georgia';
fontData[464]='Haettenschweiler';
fontData[482]='Helvetica';
fontData[483]='Impact';
fontData[484]='Lucida Handwriting';
fontData[485]='Monotype Corsiva';
fontData[486]='Tahoma';
fontData[487]='Times New Roman';
fontData[488]='Trebuchet MS';
fontData[489]='Verdana';
function selectCallback(s,changevar) 
{  
// This function gets called when selection changes  
 if( s.selectedIndex == -1 ) return;  
 var v = s.options[s.selectedIndex].value; 
 var theobjtoChange=document.getElementById(changevar);
 theobjtoChange.style.fontFamily=fontData[v];
}
 window.onload = attachBehaviors;