Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: mikefarah

cmd/root.go

@@ -212,7 +212,11 @@ yq -P -oy sample.json
 
 	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredSecurityPreferences.DisableEnvOps, "security-disable-env-ops", "", false, "Disable env related operations.")
 	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredSecurityPreferences.DisableFileOps, "security-disable-file-ops", "", false, "Disable file related operations (e.g. load)")
-	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredSecurityPreferences.EnableSystemOps, "enable-system-operator", "", false, "Enable system operator to allow execution of external commands.")
+	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredSecurityPreferences.EnableSystemOps, "security-enable-system-operator", "", false, "Enable system operator to allow execution of external commands.")
+	rootCmd.PersistentFlags().BoolVarP(&yqlib.ConfiguredSecurityPreferences.EnableSystemOps, "enable-system-operator", "", false, "DEPRECATED: use --security-enable-system-operator instead. Enable system operator to allow execution of external commands.")
+	if err = rootCmd.MarkPersistentFlagDeprecated("enable-system-operator", "use --security-enable-system-operator instead."); err != nil {
+		panic(err)
+	}
 
 	rootCmd.AddCommand(
 		createEvaluateSequenceCommand(),

pkg/yqlib/operator_system.go

@@ -33,6 +33,9 @@ func resolveCommandNode(commandNodes Context) (string, error) {
 	if cmdNode.Kind != ScalarNode || cmdNode.Tag == "!!null" {
 		return "", fmt.Errorf("system operator: command must be a string scalar")
 	}
+	if cmdNode.Value == "" {
+		return "", fmt.Errorf("system operator: command must be a non-empty string")
+	}
 	return cmdNode.Value, nil
 }
 
@@ -89,13 +92,11 @@ func systemOperator(d *dataTreeNavigator, context Context, expressionNode *Expre
 		}
 
 		var stdin bytes.Buffer
-		if candidate.Tag != "!!null" {
-			encoded, err := encodeToYamlString(candidate)
-			if err != nil {
-				return Context{}, err
-			}
-			stdin.WriteString(encoded)
+		encoded, err := encodeToYamlString(candidate)
+		if err != nil {
+			return Context{}, err
 		}
+		stdin.WriteString(encoded)
 
 		// #nosec G204 - intentional: user must explicitly enable this operator
 		cmd := exec.Command(command, args...)