Sending invalid payload to API causes panic

[richardcase]

What happened:
Sending an invalid payload to CreateMicroVM, like what you’d send to the ListMicroVMs (e.g.) { namespace: "ayx" }, crashes flintlock with the following error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0xc0 pc=0x141da69]

goroutine 164 [running]:
[github.com/weaveworks-liquidmetal/flintlock/infrastructure/grpc.convertMicroVMToModel(0x186b440](http://github.com/weaveworks-liquidmetal/flintlock/infrastructure/grpc.convertMicroVMToModel(0x186b440)?)
                /root/workspace/repos/flintlock/infrastructure/grpc/convert.go:16 +0x29
[github.com/weaveworks-liquidmetal/flintlock/infrastructure/grpc.(*server).CreateMicroVM(0xc000993b60](http://github.com/weaveworks-liquidmetal/flintlock/infrastructure/grpc.(*server).CreateMicroVM(0xc000993b60), {0x186b440, 0xc000826570}, 0xc0007ac040)
                /root/workspace/repos/flintlock/infrastructure/grpc/server.go:49 +0xb2
[github.com/weaveworks-liquidmetal/flintlock/api/services/microvm/v1alpha1._MicroVM_CreateMicroVM_Handler.func1({0x186b440](http://github.com/weaveworks-liquidmetal/flintlock/api/services/microvm/v1alpha1._MicroVM_CreateMicroVM_Handler.func1(%7B0x186b440), 0xc000826570}, {0x15f2f20?, 0xc0007ac040})
                /root/workspace/repos/flintlock/api/services/microvm/v1alpha1/microvms_grpc.pb.go:160 +0x78
[github.com/grpc-ecosystem/go-grpc-prometheus.(*ServerMetrics).UnaryServerInterceptor.func1({0x186b440](http://github.com/grpc-ecosystem/go-grpc-prometheus.(*ServerMetrics).UnaryServerInterceptor.func1(%7B0x186b440), 0xc000826570}, {0x15f2f20, 0xc0007ac040}, 0xc0006d2af0?, 0xc00000e4e0)
                /root/go/pkg/mod/[github.com/grpc-ecosystem/go-grpc-prometheus@v1.2.0/server_metrics.go:107](http://github.com/grpc-ecosystem/go-grpc-prometheus@v1.2.0/server_metrics.go:107) +0x87
[github.com/weaveworks-liquidmetal/flintlock/api/services/microvm/v1alpha1._MicroVM_CreateMicroVM_Handler({0x15b6460](http://github.com/weaveworks-liquidmetal/flintlock/api/services/microvm/v1alpha1._MicroVM_CreateMicroVM_Handler(%7B0x15b6460)?, 0xc000993b60}, {0x186b440, 0xc000826570}, 0xc0007a8120, 0xc0001a4450)
                /root/workspace/repos/flintlock/api/services/microvm/v1alpha1/microvms_grpc.pb.go:162 +0x138
[google.golang.org/grpc.(*Server).processUnaryRPC(0xc0002e88c0](http://google.golang.org/grpc.(*Server).processUnaryRPC(0xc0002e88c0), {0x1870158, 0xc0007ae4e0}, 0xc0001c6360, 0xc000993ce0, 0x21c8e60, 0x0)
                /root/go/pkg/mod/[google.golang.org/grpc@v1.47.0/server.go:1283](http://google.golang.org/grpc@v1.47.0/server.go:1283) +0xcfd
[google.golang.org/grpc.(*Server).handleStream(0xc0002e88c0](http://google.golang.org/grpc.(*Server).handleStream(0xc0002e88c0), {0x1870158, 0xc0007ae4e0}, 0xc0001c6360, 0x0)
                /root/go/pkg/mod/[google.golang.org/grpc@v1.47.0/server.go:1620](http://google.golang.org/grpc@v1.47.0/server.go:1620) +0xa1b
[google.golang.org/grpc.(*Server).serveStreams.func1.2()](http://google.golang.org/grpc.(*Server).serveStreams.func1.2())
                /root/go/pkg/mod/[google.golang.org/grpc@v1.47.0/server.go:922](http://google.golang.org/grpc@v1.47.0/server.go:922) +0x98
created by [google.golang.org/grpc.(*Server).serveStreams.func1](http://google.golang.org/grpc.(*Server).serveStreams.func1)
                /root/go/pkg/mod/[google.golang.org/grpc@v1.47.0/server.go:920](http://google.golang.org/grpc@v1.47.0/server.go:920) +0x28a

What did you expect to happen:
Sending an invalid payload should not cause a panic.

How to reproduce it:

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• flintlock version:
• containerd version:
• OS (e.g. from /etc/os-release):

[Callisto13]

reproduced: Request sent without *types.MicroVMSpec which caused a panic