#fixed code
                                @Override
    public boolean disconnect(final Endpoint endpoint) {
        final RpcClient rc = this.rpcClient;
        if (rc == null) {
            return true;
        }
        LOG.info("Disconnect from {}.", endpoint);
        rc.closeConnection(endpoint.toString());
        return true;
    }
#vulnerable code 
                                @Override
    public boolean disconnect(final Endpoint endpoint) {
        LOG.info("Disconnect from {}", endpoint);
        this.rpcClient.closeConnection(endpoint.toString());
        return true;
    } 
                            #location 4 
                            #vulnerability type THREAD_SAFETY_VIOLATION