[R4.1-36]:SLO- agent crashes when flow matches the SLO configured firewall rule

[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `/usr/bin/contrail-vrouter-agent'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x0000000000effb4e in std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState>, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState> > >::find(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
[Current thread is 1 (Thread 0x7f04a55f7700 (LWP 5552))]
(gdb) bt
#0 0x0000000000effb4e in std::_Rb_tree<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState>, std::_Select1st<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, SessionSloRuleState> > >::find(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#1 0x0000000000ef4e1c in SessionStatsCollector::UpdateSloMatchRuleEntry(boost::uuids::uuid const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#2 0x0000000000ef4fdc in SessionStatsCollector::MatchSloForSession(SessionFlowStatsInfo const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#3 0x0000000000ef7434 in SessionStatsCollector::ProcessSessionEndpoint(std::_Rb_tree_iterator<std::pair<SessionEndpointKey const, SessionEndpointInfo> > const&) ()
#4 0x0000000000ef9e35 in SessionStatsCollector::SessionTask::Run() ()
#5 0x000000000180aaad in TaskImpl::execute() ()
#6 0x00007f04ae3e1fdd in ?? () from /usr/lib/x86_64-linux-gnu/libtbb.so.2
#7 0x00007f04ae3db0dc in ?? () from /usr/lib/x86_64-linux-gnu/libtbb.so.2
#8 0x00007f04ae3d9fd3 in ?? () from /usr/lib/x86_64-linux-gnu/libtbb.so.2
#9 0x00007f04ae3d5a91 in ?? () from /usr/lib/x86_64-linux-gnu/libtbb.so.2
#10 0x00007f04ae3d5cf9 in ?? () from /usr/lib/x86_64-linux-gnu/libtbb.so.2
#11 0x00007f04ae5ff6ba in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#12 0x00007f04ad85782d in clone () from /lib/x86_64-linux-gnu/libc.so.6

version: 4.1.0.0-36, ubuntu16, newton

Test details:
- SLO at vrouter level has firewall rule configured which matches the flow.
https://nodec64.englab.juniper.net:8143/#p=setting_config_editor&q%5BobjName%5D=security-logging-object&q%5Buuid%5D=647f1529-ff27-4d07-8583-a8c7e2ace2d2

- firewall rule is to connect endpoints VN1 and VN2 with service group rules to allow only TCP.
https://nodec64.englab.juniper.net:8143/#p=setting_config_editor&q%5BobjName%5D=firewall-rule&q%5Buuid%5D=83c15c6d-1577-4576-9a11-42d24f73c522
- when ssh session is started from VM1(of VN1) to VM2(of VN2) agent crashes.