This is tracking the upstream effort needed to deliver the solution to the bug described below.

 Problem Description:

If there is a router with a policy that contains output_port only and no nexthop or nexthops then northd crashes.

                Module libgcc_s.so.1 from deb gcc-14-14.2.0-4ubuntu2~24.04.amd64
                Stack trace of thread 4130112:
                #0  0x000079ba7dd9ad1c n/a (libc.so.6 + 0x19ad1c)
                #1  0x0000569a80a770a2 build_route_policies (ovn-northd + 0x640a2)
                #2  0x0000569a80a8335c en_route_policies_run (ovn-northd + 0x7035c)
                #3  0x0000569a80aad0fe engine_recompute (ovn-northd + 0x9a0fe)
                #4  0x0000569a80aadcd5 engine_run_node (ovn-northd + 0x9acd5)
                #5  0x0000569a80a9dbe8 inc_proc_northd_run (ovn-northd + 0x8abe8)
                #6  0x0000569a80a4bc5d main (ovn-northd + 0x38c5d)
                #7  0x000079ba7dc2a1ca n/a (libc.so.6 + 0x2a1ca)
                #8  0x000079ba7dc2a28b __libc_start_main (libc.so.6 + 0x2a28b)
                #9  0x0000569a80a4cdb5 _start (ovn-northd + 0x39db5)

That is because the code assumes either nexthops or nexthop defined and then searches dots in its value

https://github.com/ovn-org/ovn/blob/main/northd/northd.c#L14745-L14766

with 
bool is_ipv4 = strchr(nexthop, '.') ? true : false;

and `nexthop` is null at that point, which segfaults.

 Impact Assessment: northd crashes fully

 Software Versions: OVN master, commit 9ef23d8c48e670878f96104a1107330f032e8e33

  Issue Type: Regression

 Reproducibility: Every time the policy above is created

 Reproduction Steps: 

Create LR with policy with output_port only, for example

_uuid               : 38891416-7999-46d3-b178-955578173c5f
action              : reroute
bfd_sessions        : []
chain               : []
external_ids        : {}
jump_chain          : []
match               : "inport==\"bgp-lrp-bgp-lr-efc1acec-4bfb-45eb-bf60-fb8fca5c9aa0-to-bgp-ls-efc1acec-4bfb-45eb-bf60-fb8fca5c9aa0-br-bgp-eth2\""
nexthop             : []
nexthops            : []
options             : {}
output_port         : 9351c7a7-172c-4ea0-9172-701718af792e
priority            : 10