TypeError 找不到错误的原因，求解答！

/*第三行报错：event.js:3Uncaught TypeError: Cannot read property 'addEventListener' of null
这是错在哪里？*/
var eventUtil={
addHandler:function(element,type,handler){
if(element.addEventListener){
element.addEventListener(type,handler,false);
}else if(element.attachEvent){
element.attachEvent("on"+type,handler);
}else{
element["on"+type] = handler;
}
},
removeHandler:function(element,type,handler){
if(element.removeEventListener){
element.removeEventListener(type,handler,false);
}else if(element.detachEvent){
element.detachEvent("on"+type,handler);
}else{
element["on"+type] = null;
}
},
getEvent:function(event){
/*var event = event || window.event;
return event;*/
return event?event:window.event;
},
getType:function(event){
return event.type;
},
getElement:function(event){
return event.target || event.srcElement;
},
preventDefault:function(event){
if(event.preventDefault){
event.preventDefault();
}else{
event.returnValue = false;
}
},
stopPropagation:function(evnt){
if(event.stopPropagation){
event.stopPropagation();
}else{
event.cancelBubble = true;
}
}
}