Dev : Java Spring + Valuelist

I've been wondering, my other Valuelist seems fine when I try to call the page. But there is one page, each time when I submit my request, it will return me:
java.lang.NullPointerException
at net.mlw.vlh.web.ValueListRequestUtil.getRequestParameterMap(ValueListRequestUtil.java:71)
at net.mlw.vlh.web.ValueListRequestUtil.buildValueListInfo(ValueListRequestUtil.java:123)
at net.mlw.vlh.web.ValueListRequestUtil.buildValueListInfo(ValueListRequestUtil.java:106)

Where the error comes from? It is from a my line of coding as below:
ValueListInfo oValueListInfo = ValueListRequestUtil.buildValueListInfo(request);

What could have been the problem? After changing here and there, finally, I've found the caused of my misery:
<form name="aForm" enctype="multipart/form-data">

Don't know what is the reason, but hoping soon to find out when free, after I remove the enctype="multipart/form-data", everything is running as usual. Ha!