#vulnerable code 
                                @Override
    public void onEvent(BlockEvent event, String fromId) {
        Block block = event.getEventBody();
        ValidateResult result = block.verify();
        if (result.isFailed()) {
            if (result.getLevel() == SeverityLevelEnum.FLAGRANT_FOUL) {
                networkService.removeNode(fromId);
            }
            return;
        }
        if (BlockBatchDownloadUtils.getInstance().downloadedBlock(fromId, block)) {
            return;
        }
        blockCacheManager.cacheBlock(block);

    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public void onEvent(BlockEvent event, String fromId) {
        Block block = event.getEventBody();
        ValidateResult result = block.verify();
        if (result.isFailed()) {
            if (result.getLevel() == SeverityLevelEnum.FLAGRANT_FOUL) {
                networkService.blackNode(fromId, NodePo.YELLOW);
            }
            return;
        }
        if (BlockBatchDownloadUtils.getInstance().downloadedBlock(fromId, block)) {
            return;
        }
        blockCacheManager.cacheBlock(block);

    }