src: fix missing file error when --watch used without argument

lib/internal/main/watch_mode.js

@@ -32,6 +32,11 @@
 prepareMainThreadExecution(false, false);
 markBootstrapComplete();
 
+if (!process.argv[1]) {
+  process.stderr.write('node: --watch requires specifying a file\n')
+  process.exit(9);
+}
+
 const kKillSignal = convertToValidSignal(getOptionValue('--watch-kill-signal'));
 const kShouldFilterModules = getOptionValue('--watch-path').length === 0;
 const kEnvFiles = [

test/parallel/test-watch-mode-without-file.mjs

@@ -0,0 +1,9 @@
+'use strict';
+
+import { spawnSync } from 'child_process';
+import { strictEqual, match } from "node:assert";
+
+const result = spawnSync(process.execPath, ['--watch'], { encoding: 'utf8' });
+
+strictEqual(result.status, 9);
+match(result.stderr, /--watch requires specifying a file/)