in RFC4760  page 9

To have a bi-directional exchange of routing information for a particular <AFI, SAFI> between a pair of BGP speakers, each such speaker MUST advertise to the other (via the Capability Advertisement mechanism) the capability to support that particular <AFI, SAFI> route.

when session up，create database listener should used negotiated adress-family。

otherwise，if peer advertised address-family which ODL bgp not support，ex：afi--BGP-LS(16388)/safi–UNICAST(1)，ODL BGP will occur nullpointerException