Panic with POST /ob/listing

[JustinDrake]

POST /ob/listing {} will panic:

13:07:11.565 [func1] [ERROR] A panic occurred in the rest api handler!
13:07:11.565 [func1] [ERROR] runtime error: invalid memory address or nil pointer dereference
goroutine 2450 [running]:
runtime/debug.Stack(0x42d874b, 0xc4202745d0, 0x1)
	/usr/local/go/src/runtime/debug/stack.go:24 +0x79
runtime/debug.PrintStack()
	/usr/local/go/src/runtime/debug/stack.go:16 +0x22
github.com/OpenBazaar/openbazaar-go/api.(*jsonAPIHandler).ServeHTTP.func1()
	/Users/justin/go/src/github.com/OpenBazaar/openbazaar-go/api/jsonapi.go:129 +0x150
panic(0x4c7e6c0, 0xc42000e0a0)
	/usr/local/go/src/runtime/panic.go:458 +0x243
github.com/OpenBazaar/openbazaar-go/api.(*jsonAPIHandler).POSTListing(0xc420094960, 0x558a680, 0xc421802410, 0xc420d4a960)
	/Users/justin/go/src/github.com/OpenBazaar/openbazaar-go/api/jsonapi.go:458 +0x110
github.com/OpenBazaar/openbazaar-go/api.post(0xc420094960, 0xc4217c54f0, 0xb, 0x558a680, 0xc421802410, 0xc420d4a960)
	/Users/justin/go/src/github.com/OpenBazaar/openbazaar-go/api/endpoints.go:26 +0xc96
github.com/OpenBazaar/openbazaar-go/api.(*jsonAPIHandler).ServeHTTP(0xc420094960, 0x558a680, 0xc421802410, 0xc420d4a960)
	/Users/justin/go/src/github.com/OpenBazaar/openbazaar-go/api/jsonapi.go:142 +0x8e8
net/http.(*ServeMux).ServeHTTP(0xc420a11b30, 0x558a680, 0xc421802410, 0xc420d4a960)
	/usr/local/go/src/net/http/server.go:2022 +0x7f
net/http.serverHandler.ServeHTTP(0xc420263a80, 0x558a680, 0xc421802410, 0xc420d4a960)
	/usr/local/go/src/net/http/server.go:2202 +0x7d
net/http.(*conn).serve(0xc420a26500, 0x558b680, 0xc420411600)
	/usr/local/go/src/net/http/server.go:1579 +0x4b7
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2293 +0x44d

[hoffmabc]

still occurring.