The problem occur when working with liberty devstack.

How to reproduce:

1)
create a security-group
remove one of it's default rule

neutron security-group-create sg1
neutron security-group-rule-delete <uuid> # one of the dafault rules

When deleting neutron security group rules, NeutronSecurityRule object is null in neutronSecurityRuleDeleted method.

2)
create a security-group
remove the security-group (securityRules list will contain null values)

neutron security-group-create sg1
neutron security-group-delete sg1

This also happens when deleting security groups. Security rules in NeutronSecurityGroup object are also null in neutronSecurityGroupDeleted method.