报出这样的错误,java.lang.NumberFormatException: For input string: "" 云课堂问答

1.各位好,写了段程序,把String型转化成Integer型,总是报出问题.但是得到的数据结果却是正确的.
2.代码:
public List<Excel> getObject(){

    Object obj=FileUtil.ReadFromExcel(); if(obj != null){ return (List<Excel>) obj; }else{               return null; } } public void check(String YN){ List<Excel> arrayList=getObject(); if(arrayList != null){ for(int i=0;i<arrayList.size();i++){ int r=Integer.parseInt(arrayList.get(i).getValue().trim()); int u=Integer.parseInt(arrayList.get(i).getChanLiang().trim()); int c=Integer.parseInt(arrayList.get(i).getPeriod().trim()); int queCount=r-(u*c); int baoCount=r-(u*7); switch(YN){ case "y":     buffer(arrayList,i,queCount,baoCount); break; case "n": System.out.println("doNothing..."); break; }                      } } }

3.总是报错:java.lang.NumberFormatException: For input string: ""
错误行数为:int r=Integer.parseInt(arrayList.get(i).getValue().trim());
4.我也百度了好多,说是要加 trim()方法,但是我这个加完后还是报错.感谢各位!!