#fixed code
                                public void release(RrdDb rrdDb) throws IOException {
        // null pointer should not kill the thread, just ignore it
        if (rrdDb == null) {
            return;
        }

        RrdEntry ref;
        try {
            ref = getEntry(rrdDb.getPath(), false);
        } catch (InterruptedException e) {
            throw new RuntimeException("release interrupted for " + rrdDb, e);
        }
        if(ref == null) {
            return;
        }

        if (ref.count <= 0) {
            passNext(ACTION.DROP, ref);
            throw new IllegalStateException("Could not release [" + rrdDb.getPath() + "], the file was never requested");
        }
        if (--ref.count == 0) {
            if(ref.rrdDb == null) {
                passNext(ACTION.DROP, ref);
                throw new IllegalStateException("Could not release [" + rrdDb.getPath() + "], pool corruption");                    
            }
            ref.rrdDb.close();
            passNext(ACTION.DROP, ref);                
            //If someone is waiting for an empty entry, signal it
            ref.waitempty.countDown();
        } else {
            passNext(ACTION.SWAP, ref);
        }
    }
#vulnerable code 
                                public void release(RrdDb rrdDb) throws IOException {
        // null pointer should not kill the thread, just ignore it
        if (rrdDb == null) {
            return;
        }

        RrdEntry ref;
        try {
            ref = getEntry(rrdDb.getPath(), false);
        } catch (InterruptedException e) {
            throw new RuntimeException("release interrupted for " + rrdDb, e);
        }
        if(ref == null) {
            return;
        }

        if (ref.count <= 0) {
            passNext(ACTION.DROP, ref);
            throw new IllegalStateException("Could not release [" + rrdDb.getPath() + "], the file was never requested");
        }
        if (--ref.count == 0) {
            if(ref.rrdDb == null) {
                passNext(ACTION.DROP, ref);
                throw new IllegalStateException("Could not release [" + rrdDb.getPath() + "], pool corruption");                    
            }
            ref.rrdDb.close();
            usage.decrementAndGet();
            try {
                countLock.lockInterruptibly();
                if(usage.get() < maxCapacity) {
                    full.signal();
                }
                countLock.unlock();
            } catch (InterruptedException e) {
                throw new RuntimeException("release interrupted for " + rrdDb, e);
            } finally {
                passNext(ACTION.DROP, ref);                
            }
            //If someone is waiting for an empty entry, signal it
            ref.waitempty.countDown();
        } else {
            passNext(ACTION.SWAP, ref);
        }
    } 
                            #location 21 
                            #vulnerability type THREAD_SAFETY_VIOLATION