#fixed code
                                @Test
    public void testGetGroupChannelTable() throws Exception {
        producerManager.registerProducer(group, clientInfo);
        Map<Channel, ClientChannelInfo> oldMap = producerManager.getGroupChannelTable().get(group);
        
        producerManager.unregisterProducer(group, clientInfo);
        assertThat(oldMap.size()).isEqualTo(0);
    }
#vulnerable code 
                                @Test
    public void testGetGroupChannelTable() throws Exception {
        producerManager.registerProducer(group, clientInfo);
        HashMap<Channel, ClientChannelInfo> oldMap = producerManager.getGroupChannelTable().get(group);
        
        producerManager.unregisterProducer(group, clientInfo);
        assertThat(oldMap.size()).isNotEqualTo(0);
    } 
                            #location 7 
                            #vulnerability type NULL_DEREFERENCE