I met another panic while stress testing.
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x5e7b0]

goroutine 28 [running]:
runtime.panic(0x2d3a50, 0x46588b)
	/usr/lib/go/src/pkg/runtime/panic.c:279 +0x1a0
net/http.Header.sortedKeyValues(0x9442c5e0, 0x94324580, 0x0, 0x0, 0x2, 0x94430020)
	/usr/lib/go/src/pkg/net/http/header.go:135 +0x2e8
net/http.Header.WriteSubset(0x9442c5e0, 0x841d6860, 0x9442cc20, 0x94324580, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/header.go:150 +0xec
net/http.(*Request).write(0x943024d0, 0x841d6860, 0x9442cc20, 0x841d6800, 0x9442c700, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/request.go:420 +0x698
net/http.(*persistConn).writeLoop(0x94306c60)
	/usr/lib/go/src/pkg/net/http/transport.go:891 +0x1cc
created by net/http.(*Transport).dialConn
	/usr/lib/go/src/pkg/net/http/transport.go:601 +0x884

goroutine 16 [syscall]:
launchpad.net/go-unityscopes/v2._Cfunc_run_scope(0x943363b0, 0x943360f0, 0x94336108, 0x943363a8, 0x943363b8)
	launchpad.net/go-unityscopes/v2/_obj/_cgo_defun.c:667 +0x34
launchpad.net/go-unityscopes/v2.Run(0x841d14a8, 0x94330300, 0x0, 0x0)
	/home/enwei/go/src/launchpad.net/go-unityscopes/v2/unityscope.go:257 +0x31c
main.main()
	/home/enwei/scopes/yelp-scope/src/yelp.go:692 +0x1d0

goroutine 19 [finalizer wait]:
runtime.park(0x438fc, 0x479a2c, 0x467e51)
	/usr/lib/go/src/pkg/runtime/proc.c:1369 +0x5c
runtime.parkunlock(0x479a2c, 0x467e51)
	/usr/lib/go/src/pkg/runtime/proc.c:1385 +0x40
runfinq()
	/usr/lib/go/src/pkg/runtime/mgc0.c:2644 +0xa0
runtime.goexit()
	/usr/lib/go/src/pkg/runtime/proc.c:1445

goroutine 17 [syscall]:
runtime.goexit()
	/usr/lib/go/src/pkg/runtime/proc.c:1445

goroutine 18 [syscall]:
runtime.goexit()
	/usr/lib/go/src/pkg/runtime/proc.c:1445

goroutine 20 [select]:
net/http.(*persistConn).roundTrip(0x94306cc0, 0x9442f1b0, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:1015 +0x634
net/http.(*Transport).RoundTrip(0x94306240, 0x943038f0, 0xf9ab0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:208 +0x388
net/http.send(0x943038f0, 0x841d13d0, 0x94306240, 0x943039d0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:195 +0x378
net/http.(*Client).send(0x9442c880, 0x943038f0, 0x6d, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:118 +0x140
net/http.(*Client).doFollowingRedirects(0x9442c880, 0x943038f0, 0x3773a8, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:343 +0x808
net/http.(*Client).Do(0x9442c880, 0x943038f0, 0x94303810, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:150 +0xb4
main.(*YelpScope).get(0x94330300, 0x9442c840, 0x275e80, 0x9442c820, 0x0, 0x0)
	/home/enwei/scopes/yelp-scope/src/yelp.go:189 +0x144
main.(*YelpScope).Search(0x94330300, 0x943363e0, 0x943363f0, 0x9433c4d0, 0x94330400, 0x0, 0x0)
	/home/enwei/scopes/yelp-scope/src/yelp.go:315 +0x2400
launchpad.net/go-unityscopes/v2.func·002()
	/home/enwei/go/src/launchpad.net/go-unityscopes/v2/unityscope.go:70 +0x80
created by launchpad.net/go-unityscopes/v2.callScopeSearch
	/home/enwei/go/src/launchpad.net/go-unityscopes/v2/unityscope.go:76 +0x150

goroutine 21 [select]:
net/http.(*persistConn).roundTrip(0x94306c60, 0x9442e140, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:1015 +0x634
net/http.(*Transport).RoundTrip(0x94306240, 0x943024d0, 0xf9ab0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:208 +0x388
net/http.send(0x943024d0, 0x841d13d0, 0x94306240, 0x94306960, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:195 +0x378
net/http.(*Client).send(0x9442c360, 0x943024d0, 0x54, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:118 +0x140
net/http.(*Client).doFollowingRedirects(0x9442c360, 0x943024d0, 0x3773a8, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:343 +0x808
net/http.(*Client).Do(0x9442c360, 0x943024d0, 0x943064e0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/client.go:150 +0xb4
main.(*YelpScope).get(0x94330300, 0x9442c320, 0x275e80, 0x9442c300, 0x0, 0x0)
	/home/enwei/scopes/yelp-scope/src/yelp.go:189 +0x144
main.(*YelpScope).Search(0x94330300, 0x94336378, 0x943363a0, 0x9433c048, 0x94330580, 0x0, 0x0)
	/home/enwei/scopes/yelp-scope/src/yelp.go:315 +0x2400
launchpad.net/go-unityscopes/v2.func·002()
	/home/enwei/go/src/launchpad.net/go-unityscopes/v2/unityscope.go:70 +0x80
created by launchpad.net/go-unityscopes/v2.callScopeSearch
	/home/enwei/go/src/launchpad.net/go-unityscopes/v2/unityscope.go:76 +0x150

goroutine 29 [IO wait]:
net.runtime_pollWait(0x841d6738, 0x72, 0x0)
	/usr/lib/go/src/pkg/runtime/netpoll.goc:146 +0x6c
net.(*pollDesc).Wait(0x94330a78, 0x72, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/fd_poll_runtime.go:84 +0x44
net.(*pollDesc).WaitRead(0x94330a78, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/fd_poll_runtime.go:89 +0x40
net.(*netFD).Read(0x94330a40, 0x9444d000, 0x1000, 0x1000, 0x0, 0x841d12c8, 0xb)
	/usr/lib/go/src/pkg/net/fd_unix.go:242 +0x320
net.(*conn).Read(0x9442f248, 0x9444d000, 0x1000, 0x1000, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/net.go:122 +0xd4
net/http.noteEOFReader.Read(0x841d6818, 0x9442f248, 0x94306cec, 0x9444d000, 0x1000, 0x1000, 0x48944c, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:1203 +0x80
net/http.(*noteEOFReader).Read(0x94430510, 0x9444d000, 0x1000, 0x1000, 0x1ec, 0x0, 0x0)
	<autogenerated>:124 +0xdc
bufio.(*Reader).fill(0x94310ba0)
	/usr/lib/go/src/pkg/bufio/bufio.go:97 +0x1cc
bufio.(*Reader).Peek(0x94310ba0, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/bufio/bufio.go:132 +0xdc
net/http.(*persistConn).readLoop(0x94306cc0)
	/usr/lib/go/src/pkg/net/http/transport.go:782 +0x90
created by net/http.(*Transport).dialConn
	/usr/lib/go/src/pkg/net/http/transport.go:600 +0x85c

goroutine 27 [IO wait]:
net.runtime_pollWait(0x841d67a8, 0x72, 0x0)
	/usr/lib/go/src/pkg/runtime/netpoll.goc:146 +0x6c
net.(*pollDesc).Wait(0x94330838, 0x72, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/fd_poll_runtime.go:84 +0x44
net.(*pollDesc).WaitRead(0x94330838, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/fd_poll_runtime.go:89 +0x40
net.(*netFD).Read(0x94330800, 0x9443b000, 0x1000, 0x1000, 0x0, 0x841d12c8, 0xb)
	/usr/lib/go/src/pkg/net/fd_unix.go:242 +0x320
net.(*conn).Read(0x9442f1f8, 0x9443b000, 0x1000, 0x1000, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/net.go:122 +0xd4
net/http.noteEOFReader.Read(0x841d6818, 0x9442f1f8, 0x94306c8c, 0x9443b000, 0x1000, 0x1000, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/net/http/transport.go:1203 +0x80
net/http.(*noteEOFReader).Read(0x944304c0, 0x9443b000, 0x1000, 0x1000, 0x83744eff, 0x0, 0x0)
	<autogenerated>:124 +0xdc
bufio.(*Reader).fill(0x94310b10)
	/usr/lib/go/src/pkg/bufio/bufio.go:97 +0x1cc
bufio.(*Reader).Peek(0x94310b10, 0x1, 0x0, 0x0, 0x0, 0x0, 0x0)
	/usr/lib/go/src/pkg/bufio/bufio.go:132 +0xdc
net/http.(*persistConn).readLoop(0x94306c60)
	/usr/lib/go/src/pkg/net/http/transport.go:782 +0x90
created by net/http.(*Transport).dialConn
	/usr/lib/go/src/pkg/net/http/transport.go:600 +0x85c

goroutine 30 [select]:
net/http.(*persistConn).writeLoop(0x94306cc0)
	/usr/lib/go/src/pkg/net/http/transport.go:885 +0x2d4
created by net/http.(*Transport).dialConn
	/usr/lib/go/src/pkg/net/http/transport.go:601 +0x884
[2016-09-28 22:25:52.370] INFO: Registry: RegistryObject::ScopeProcess::on_process_death(): Process for scope: "com.canonical.scopes.yelp_yelp" exited
[2016-09-28 22:25:52.370] ERROR: Registry: RegistryObject::ScopeProcess: Scope: "com.canonical.scopes.yelp_yelp" closed unexpectedly. Either the process crashed or was killed forcefully.
query complete, status:  ok