Vault 1.2.1 is crashing when trying to authenticate with radius auth method

[2easy]

Describe the bug
After upgrade to 1.2.1 Vault is crashing when trying to authenticate with Radius server.

To Reproduce
Steps to reproduce the behavior:

1. Run vault auth enable radius
2. Run vault write auth/radius/config host=radius.internal dial_timeout=10 nas_port=10 port=1812 read_timeout=10 unregistered_user_policies="" secret=supersecret
3. Run echo -n "$PASSWORD-$TOKEN" | vault login -method=userpass -path=radius username=$VUSER password=-

Expected behavior
I should be able to log in via this enpoint as in previous version 1.0.3

Environment:

• Vault Server Version (retrieve with vault status): 1.2.1
• Vault CLI Version (retrieve with vault version): 1.2.1
• Server Operating System/Architecture: Debian Stretch amd64

Vault server configuration file(s):

None

Additional context

2019-08-09T08:25:45.988+0200 [INFO]  http: panic serving 127.0.0.1:40002: runtime error: invalid memory address or nil pointer dereference
goroutine 714 [running]:
net/http.(*conn).serve.func1(0xc0000cc820)
	/goroot/src/net/http/server.go:1769 +0x139
panic(0x2c13560, 0x5b6b250)
	/goroot/src/runtime/panic.go:522 +0x1b5
github.com/hashicorp/vault/builtin/credential/radius.(*backend).pathLogin(0xc000aaa018, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0xc0001d5890, 0x10, 0xc0001d5890, 0xc0009d0b20)
	/gopath/src/github.com/hashicorp/vault/builtin/credential/radius/path_login.go:127 +0x74a
github.com/hashicorp/vault/helper/mfa.(*backend).wrapLoginHandler.func1(0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0xc0001d5890, 0xc0002450c8, 0x5b7b67, 0xc0009d0d10)
	/gopath/src/github.com/hashicorp/vault/helper/mfa/mfa.go:69 +0x61
github.com/hashicorp/vault/vendor/github.com/hashicorp/vault/sdk/framework.(*Backend).HandleRequest(0xc0002455f0, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0x0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/vendor/github.com/hashicorp/vault/sdk/framework/backend.go:253 +0x492
github.com/hashicorp/vault/builtin/plugin.(*PluginBackend).HandleRequest.func1(0x0, 0x28)
	/gopath/src/github.com/hashicorp/vault/builtin/plugin/backend.go:198 +0x5a
github.com/hashicorp/vault/builtin/plugin.(*PluginBackend).lazyLoadBackend(0xc000b1b9a0, 0x37b8580, 0xc0008d9980, 0x37b9000, 0xc0008cce80, 0xc0009d0e20, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/builtin/plugin/backend.go:160 +0x8c
github.com/hashicorp/vault/builtin/plugin.(*PluginBackend).HandleRequest(0xc000b1b9a0, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0x0, 0xc0008baec0, 0xc)
	/gopath/src/github.com/hashicorp/vault/builtin/plugin/backend.go:196 +0xbb
github.com/hashicorp/vault/vault.(*Router).routeCommon(0xc0003db040, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0x0, 0x0, 0x0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/vault/router.go:676 +0x919
github.com/hashicorp/vault/vault.(*Router).Route(...)
	/gopath/src/github.com/hashicorp/vault/vault/router.go:476
github.com/hashicorp/vault/vault.(*Core).doRouting(0xc00010bb80, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0xc000a4a0f0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/vault/request_handling.go:558 +0x5a
github.com/hashicorp/vault/vault.(*Core).handleLoginRequest(0xc00010bb80, 0x37b8580, 0xc0008d9980, 0xc00004e8c0, 0x0, 0x0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/vault/request_handling.go:977 +0xacc
github.com/hashicorp/vault/vault.(*Core).handleCancelableRequest(0xc00010bb80, 0x37b8580, 0xc0008d9980, 0x5b70a40, 0xc00004e8c0, 0x5b70a40, 0x37b8580, 0xc0008d9980)
	/gopath/src/github.com/hashicorp/vault/vault/request_handling.go:448 +0x1ed
github.com/hashicorp/vault/vault.(*Core).switchedLockHandleRequest(0xc00010bb80, 0x37b8580, 0xc0008d97a0, 0xc00004e8c0, 0x1, 0x0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/vault/request_handling.go:417 +0x288
github.com/hashicorp/vault/vault.(*Core).HandleRequest(...)
	/gopath/src/github.com/hashicorp/vault/vault/request_handling.go:382
github.com/hashicorp/vault/http.request(0xc00010bb80, 0x37992c0, 0xc00012c000, 0xc0001db600, 0xc00004e8c0, 0x0, 0x0)
	/gopath/src/github.com/hashicorp/vault/http/handler.go:620 +0x80
github.com/hashicorp/vault/http.handleLogicalInternal.func1(0x37992c0, 0xc00012c000, 0xc0001db600)
	/gopath/src/github.com/hashicorp/vault/http/logical.go:278 +0x32d
net/http.HandlerFunc.ServeHTTP(0xc000a71580, 0x37992c0, 0xc00012c000, 0xc0001db600)
	/goroot/src/net/http/server.go:1995 +0x44
github.com/hashicorp/vault/http.handleRequestForwarding.func1(0x37992c0, 0xc00012c000, 0xc0001db600)
	/gopath/src/github.com/hashicorp/vault/http/handler.go:545 +0x2b7
net/http.HandlerFunc.ServeHTTP(0xc000a715a0, 0x37992c0, 0xc00012c000, 0xc0001db600)
	/goroot/src/net/http/server.go:1995 +0x44
net/http.(*ServeMux).ServeHTTP(0xc0007375c0, 0x37992c0, 0xc00012c000, 0xc0001db600)
	/goroot/src/net/http/server.go:2375 +0x1d6
github.com/hashicorp/vault/http.wrapHelpHandler.func1(0x37992c0, 0xc00012c000, 0xc0001db600)
	/gopath/src/github.com/hashicorp/vault/http/help.go:24 +0x156
net/http.HandlerFunc.ServeHTTP(0xc000a71640, 0x37992c0, 0xc00012c000, 0xc0001db600)
	/goroot/src/net/http/server.go:1995 +0x44
github.com/hashicorp/vault/http.wrapCORSHandler.func1(0x37992c0, 0xc00012c000, 0xc0001db600)
	/gopath/src/github.com/hashicorp/vault/http/cors.go:29 +0x9e1
net/http.HandlerFunc.ServeHTTP(0xc000a71660, 0x37992c0, 0xc00012c000, 0xc0001db600)
	/goroot/src/net/http/server.go:1995 +0x44
github.com/hashicorp/vault/http.wrapGenericHandler.func1(0x37992c0, 0xc00012c000, 0xc0001db400)
	/gopath/src/github.com/hashicorp/vault/http/handler.go:204 +0x339
net/http.HandlerFunc.ServeHTTP(0xc000a74b10, 0x37992c0, 0xc00012c000, 0xc0001db400)
	/goroot/src/net/http/server.go:1995 +0x44
github.com/hashicorp/vault/vendor/github.com/hashicorp/go-cleanhttp.PrintablePathCheckHandler.func1(0x37992c0, 0xc00012c000, 0xc0001db400)
	/gopath/src/github.com/hashicorp/vault/vendor/github.com/hashicorp/go-cleanhttp/handlers.go:42 +0xbb
net/http.HandlerFunc.ServeHTTP(0xc000a71680, 0x37992c0, 0xc00012c000, 0xc0001db400)
	/goroot/src/net/http/server.go:1995 +0x44
net/http.serverHandler.ServeHTTP(0xc000b14dd0, 0x37992c0, 0xc00012c000, 0xc0001db400)
	/goroot/src/net/http/server.go:2774 +0xa8
net/http.(*conn).serve(0xc0000cc820, 0x37b84c0, 0xc000216b80)
	/goroot/src/net/http/server.go:1878 +0x851
created by net/http.(*Server).Serve
	/goroot/src/net/http/server.go:2884  #+0x2f4

[ncabatoff]

Hi @2easy,

Thanks for the detailed bug report. We'll include a fix in 1.2.2.