Comment 2 for bug 1621451

I have seen this error before when patch [1] just merged. I update the code, and restart the df-controller, the error show up. However, after restart neutron-server, the error has gone. And I never see the error again. So I think it should not be a bug now, unless more details are provided.

[1] 2f81efdf21557b810867b5eaa3bf477cab9b1b52