Exception in bbsim during ONU poweron

./bbsimctl onu shutdown BBSM00040001
then
./bbsimctl onu poweron BBSM00040001
and got the exception below.

time="2020-01-05T23:49:04-08:00" level=info msg="Received request to shutdown ONU" OnuSn=BBSM00040001 module=GrpcApiServer
time="2020-01-05T23:49:04-08:00" level=debug msg="Changing ONU InternalState from enabled to disabled" IntfId=0 OnuId=1 OnuSn=BBSM00040001 module=ONU
time="2020-01-05T23:49:04-08:00" level=trace msg="Received message on ONU Channel" messageType=DyingGaspIndication module=ONU onuID=1 onuSN=BBSM00040001
time="2020-01-05T23:49:04-08:00" level=info msg=sendDyingGaspInd IntfId=0 OnuId=1 OnuSn=BBSM00040001 module=ONU
time="2020-01-05T23:49:04-08:00" level=trace msg="Received message on ONU Channel" messageType=OnuIndication module=ONU onuID=1 onuSN=BBSM00040001
time="2020-01-05T23:49:04-08:00" level=debug msg="Sent Indication_OnuInd" AdminState=down IntfId=0 OnuId=1 OnuSn=BBSM00040001 OperState=down module=ONU
time="2020-01-05T23:49:04-08:00" level=trace msg="ONU message handling canceled via channel close" module=ONU onuID=1 onuSN=BBSM00040001
time="2020-01-05T23:49:04-08:00" level=debug msg="Stopped handling ONU Indication Channel" module=ONU onuID=1 onuSN=BBSM00040001
time="2020-01-05T23:49:39-08:00" level=info msg="Received request to poweron ONU" OnuSn=BBSM00040001 module=GrpcApiServer
fatal error: sync: RUnlock of unlocked RWMutex

goroutine 517 [running]:
runtime.throw(0xcba21a, 0x21)
/usr/local/go/src/runtime/panic.go:617 +0x72 fp=0xc000481298 sp=0xc000481268 pc=0x42f712
sync.throw(0xcba21a, 0x21)
/usr/local/go/src/runtime/panic.go:603 +0x35 fp=0xc0004812b8 sp=0xc000481298 pc=0x42f695
sync.(*RWMutex).RUnlock(0xc0000e5478)
/usr/local/go/src/sync/rwmutex.go:71 +0x51 fp=0xc0004812d8 sp=0xc0004812b8 pc=0x473361
runtime.call32(0x0, 0xcda0e8, 0xc0005844b0, 0x800000008)
/usr/local/go/src/runtime/asm_amd64.s:519 +0x3b fp=0xc000481308 sp=0xc0004812d8 pc=0x45ac3b
panic(0xbad520, 0xdc2830)
/usr/local/go/src/runtime/panic.go:522 +0x1b5 fp=0xc000481398 sp=0xc000481308 pc=0x42f245
runtime.chansend(0xc0000e5620, 0xc000481478, 0xc000481401, 0xad82dd, 0xc000676220)
/usr/local/go/src/runtime/chan.go:187 +0x5f5 fp=0xc000481418 sp=0xc000481398 pc=0x4088e5
runtime.chansend1(0xc0000e5620, 0xc000481478)
/usr/local/go/src/runtime/chan.go:127 +0x35 fp=0xc000481450 sp=0xc000481418 pc=0x4082e5
github.com/opencord/bbsim/internal/bbsim/devices.CreateONU.func5(0xc00062a150)
/bbsim/internal/bbsim/devices/onu.go:167 +0xad fp=0xc0004814b8 sp=0xc000481450 pc=0xad82dd
github.com/looplab/fsm.(*FSM).enterStateCallbacks(0xc0000e5440, 0xc00062a150)
/bbsim/vendor/github.com/looplab/fsm/fsm.go:403 +0x101 fp=0xc000481508 sp=0xc0004814b8 pc=0x8c2d91
github.com/looplab/fsm.(*FSM).Event.func1()
/bbsim/vendor/github.com/looplab/fsm/fsm.go:308 +0x9e fp=0xc000481550 sp=0xc000481508 pc=0x8c2f5e
github.com/looplab/fsm.transitionerStruct.transition(...)
/bbsim/vendor/github.com/looplab/fsm/fsm.go:354
github.com/looplab/fsm.(*transitionerStruct).transition(0x1aff698, 0xc0000e5440, 0x0, 0x0)
<autogenerated>:1 +0x65 fp=0xc000481560 sp=0xc000481550 pc=0x8c3075
github.com/looplab/fsm.(*FSM).doTransition(...)
/bbsim/vendor/github.com/looplab/fsm/fsm.go:339
github.com/looplab/fsm.(*FSM).Event(0xc0000e5440, 0xc90507, 0x6, 0x0, 0x0, 0x0, 0x0, 0x0)
/bbsim/vendor/github.com/looplab/fsm/fsm.go:321 +0x582 fp=0xc0004816a0 sp=0xc000481560 pc=0x8c2342
github.com/opencord/bbsim/internal/bbsim/api.BBSimServer.PoweronONU(0xde2160, 0xc00068e210, 0xc00068e240, 0xc4d020, 0xc00060c400, 0xdef0a0)
/bbsim/internal/bbsim/api/onus_handler.go:145 +0x2d8 fp=0xc000481b28 sp=0xc0004816a0 pc=0xae0268
github.com/opencord/bbsim/internal/bbsim/api.(*BBSimServer).PoweronONU(0x1aff698, 0xde2160, 0xc00068e210, 0xc00068e240, 0x1aff698, 0xc00068e210, 0xc000555bc8)
<autogenerated>:1 +0x50 fp=0xc000481b68 sp=0xc000481b28 pc=0xae21c0
github.com/opencord/bbsim/api/bbsim._BBSim_PoweronONU_Handler(0xc4d020, 0x1aff698, 0xde2160, 0xc00068e210, 0xc00060c480, 0x0, 0xde2160, 0xc00068e210, 0xc000690050, 0xe)
/bbsim/api/bbsim/bbsim.pb.go:998 +0x23e fp=0xc000481bd8 sp=0xc000481b68 pc=0x87beee
google.golang.org/grpc.(*Server).processUnaryRPC(0xc000388300, 0xdec460, 0xc0003a5800, 0xc00036e000, 0xc0003a6210, 0x1571ff8, 0x0, 0x0, 0x0)
/bbsim/vendor/google.golang.org/grpc/server.go:999 +0x466 fp=0xc000481e50 sp=0xc000481bd8 pc=0x8605d6
google.golang.org/grpc.(*Server).handleStream(0xc000388300, 0xdec460, 0xc0003a5800, 0xc00036e000, 0x0)
/bbsim/vendor/google.golang.org/grpc/server.go:1279 +0xda6 fp=0xc000481f80 sp=0xc000481e50 pc=0x8644e6
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc000686000, 0xc000388300, 0xdec460, 0xc0003a5800, 0xc00036e000)
/bbsim/vendor/google.golang.org/grpc/server.go:717 +0x9f fp=0xc000481fb8 sp=0xc000481f80 pc=0x870c1f
runtime.goexit()
/usr/local/go/src/runtime/asm_amd64.s:1337 +0x1 fp=0xc000481fc0 sp=0xc000481fb8 pc=0x45c951
created by google.golang.org/grpc.(*Server).serveStreams.func1
/bbsim/vendor/google.golang.org/grpc/server.go:715 +0xa1