fixed NPE when cache folder is empty

InFileObjectPersister throws NPE from line 112

        List<Object> result = new ArrayList<Object>(cacheFileNameList.length);

The problem is with the 'cacheFileNameList'  array that is returned from the following line

String[] cacheFileNameList = getCacheFolder().list(new FilenameFilter() {

if this array is null which could be true in some situations than a NPE is thrown on line 112. 

It can be reproduced by clearing app cache from settings and try to use the app, you will see app crash.