JXLS求救 IF TAG！！！！！急

<jx:if test='${variance_type == "staff" }'>
  a
</jx:if>报表里面有1行，如果我把variance_type 设成 staff就OK
如果把variance_type 设成 staff2就报错空值？？？？怎么回事java.lang.NullPointerException
java.util.TreeMap.compare(TreeMap.java:1085)
java.util.TreeMap.getEntry(TreeMap.java:345)
java.util.TreeMap.remove(TreeMap.java:504)
org.apache.poi.hssf.usermodel.HSSFSheet.removeRow(HSSFSheet.java:214)
net.sf.jxls.util.TagBodyHelper.removeBodyRows(TagBodyHelper.java:182)
net.sf.jxls.controller.SheetTransformationControllerImpl.removeBodyRows(SheetTransformationControllerImpl.java:94)
net.sf.jxls.tag.IfTag.process(IfTag.java:80)
net.sf.jxls.transformer.TagRowTransformer.transform(TagRowTransformer.java:36)
net.sf.jxls.transformer.SheetTransformer.transformSheet(SheetTransformer.java:95)
net.sf.jxls.transformer.XLSTransformer.transformXLS(XLSTransformer.java:214)
com.freeborders.psa.servlet.JXLSReportServlet.service(JXLSReportServlet.java:60)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:455)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:279)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
com.freeborders.psa.servlet.EncodingFilter.doFilter(EncodingFilter.java:165)
com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:39)