mdatagen: avoid panic when run without arguments

.chloggen/mdatagen-no-panic.yaml

@@ -0,0 +1,4 @@
+change_type: bug_fix
+component: cmd/mdatagen
+note: Fix panic when mdatagen is run without arguments.
+issues: [14506]

cmd/mdatagen/internal/command.go

@@ -59,6 +59,7 @@ func NewCommand() (*cobra.Command, error) {
 		Use:          "mdatagen",
 		Version:      ver,
 		SilenceUsage: true,
+		Args:         cobra.ExactArgs(1),
 		RunE: func(_ *cobra.Command, args []string) error {
 			return run(args[0])
 		},

cmd/mdatagen/internal/command_test.go

@@ -29,6 +29,16 @@ func TestNewCommand(t *testing.T) {
 	assert.True(t, cmd.SilenceUsage)
 }
 
+func TestCommandNoArgs(t *testing.T) {
+	cmd, err := NewCommand()
+	require.NoError(t, err)
+
+	cmd.SetArgs([]string{})
+	err = cmd.Execute()
+
+	require.Error(t, err)
+}
+
 func TestRunContents(t *testing.T) {
 	tests := []struct {
 		yml                  string