When I flush gruop from cache(flushGroup(groupName)), and this group is not in cache, I get exception:
java.lang.NullPointerException
at java.util.HashSet.<init>(HashSet.java:99)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.getGroupForReading(AbstractConcurrentReadCache.java:954)
at com.opensymphony.oscache.base.algorithm.AbstractConcurrentReadCache.getGroup(AbstractConcurrentReadCache.java:372)
at com.opensymphony.oscache.base.Cache.flushGroup(Cache.java:447)
at com.opensymphony.oscache.base.Cache.flushGroup(Cache.java:434)
..................................................

this is problem. You should check, if group exists and then flush it. But You don't check and exception. wrrr