Check if sys view is missing in GRPC sys view (#18210)

And return an error instead of panicking.

This situation can occur if a plugin attempts to access the system
view during setup when Vault is checking the plugin metadata.

Fixes #17878.

sdk/plugin/grpc_system_test.go

@@ -6,7 +6,7 @@ import (
 	"testing"
 	"time"
 
-	plugin "github.com/hashicorp/go-plugin"
+	"github.com/hashicorp/go-plugin"
 	"github.com/hashicorp/vault/sdk/helper/consts"
 	"github.com/hashicorp/vault/sdk/logical"
 	"github.com/hashicorp/vault/sdk/plugin/pb"
@@ -14,6 +14,13 @@ import (
 	"google.golang.org/protobuf/proto"
 )
 
+func TestSystem_GRPC_ReturnsErrIfSystemViewNil(t *testing.T) {
+	_, err := new(gRPCSystemViewServer).ReplicationState(context.Background(), nil)
+	if err == nil {
+		t.Error("Expected error when using server with no impl")
+	}
+}
+
 func TestSystem_GRPC_GRPC_impl(t *testing.T) {
 	var _ logical.SystemView = new(gRPCSystemViewClient)
 }