#vulnerable code 
                                @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        
        final UnitOfWork unitOfWork;
        
        // Only start a new unit of work if the entitymanager is empty
        // otherwise someone else has started the unit of work already
        // and we do nothing
        // Please compare to com.google.inject.persist.jpa.JpaLocalTxnInterceptor
        // we just mimick that interceptor
        //
        // IMPORTANT:
        // Nesting of begin() end() of unitOfWork is NOT allowed. Contrary to
        // the documentation of Google Guice as of March 2014.
        // Related Ninja issue: https://github.com/ninjaframework/ninja/issues/157
        if (entityManagerProvider.get() == null) {
        
            unitOfWork = unitOfWorkProvider.get();
            unitOfWork.begin();
            didWeStartWork.set(Boolean.TRUE);

        } else {
            // If unit of work already started we don't do anything here...
            // another UnitOfWorkInterceptor point point will take care...
            // This happens if you are nesting your calls.
            return invocation.proceed();
        }

        try {

            return invocation.proceed();

        } finally {

            if (null != didWeStartWork.get()) {
                
                didWeStartWork.remove();
                unitOfWork.end();
                
            }

        }

    } 
                            #location 19 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        
        if (null == didWeStartWork.get()) {
            
            unitOfWork.begin();
            didWeStartWork.set(Boolean.TRUE);
            
        } else {
            // If unit of work already started we don't do anything here...
            // another UnitOfWorkInterceptor point point will take care...
            // This happens if you are nesting your calls.
            return invocation.proceed();
        }

        try {

            return invocation.proceed();

        } finally {

            if (null != didWeStartWork.get()) {
                
                didWeStartWork.remove();
                unitOfWork.end();
                
            }

        }

    }