chore: prevent nil dereferences on cmd handlers (#8319)

* chore: detect nil cmd handlers

Prevent nil panic dereferences on cmd handlers. Add a unit test
to prevent future mistakes

enterprise/cli/provisionerdaemons.go

@@ -27,6 +27,9 @@ func (r *RootCmd) provisionerDaemons() *clibase.Cmd {
 	cmd := &clibase.Cmd{
 		Use:   "provisionerd",
 		Short: "Manage provisioner daemons",
+		Handler: func(inv *clibase.Invocation) error {
+			return inv.Command.HelpHandler(inv)
+		},
 		Children: []*clibase.Cmd{
 			r.provisionerDaemonStart(),
 		},

enterprise/cli/root_test.go

@@ -17,3 +17,13 @@ func newCLI(t *testing.T, args ...string) (*clibase.Invocation, config.Root) {
 	require.NoError(t, err)
 	return clitest.NewWithCommand(t, cmd, args...)
 }
+
+func TestEnterpriseHandlersOK(t *testing.T) {
+	t.Parallel()
+
+	var root cli.RootCmd
+	cmd, err := root.Command(root.EnterpriseSubcommands())
+	require.NoError(t, err)
+
+	clitest.HandlersOK(t, cmd)
+}