fix(cli): do not crash on no rules configured

bin/cli.js

@@ -60,8 +60,13 @@ if (module === require.main) {
     })
   )
     .then((configs) => {
-      const rules = configs.flatMap(({ rules }, index) =>
-        Object.entries(rules).map((entry) => [...entry, args[index]])
+      const rules = configs.flatMap(
+        (
+          // Initializing config and rules for files that aren't included in the flat config,
+          // which is a very unlikely scenario, but should still be treated as a success
+          { rules = {} } = {},
+          index
+        ) => Object.entries(rules).map((entry) => [...entry, args[index]])
       );
       const result = processRules(rules);
       if (result.stderr) {

test/cli.test.js

@@ -1,5 +1,7 @@
 "use strict";
 
+const childProcess = require("child_process");
+const path = require("path");
 const cli = require("../bin/cli");
 
 const offPatterns = [0, "off", [0], ["off"], ["off", "never"]];
@@ -76,6 +78,14 @@ test("no results", () => {
   `);
 });
 
+test("empty config", (done) => {
+  childProcess.exec(
+    `node ${path.join(process.cwd(), "bin/cli.js")} index.js`,
+    { cwd: path.join(__dirname, "fixtures/empty-config") },
+    done
+  );
+});
+
 test("conflicting options", () => {
   const rules = ["strict", ["curly", "multi-line"]];
   expect(cli.processRules(createRules(rules, "error"))).toMatchInlineSnapshot(`

test/fixtures/empty-config/eslint.config.mjs

@@ -0,0 +1 @@
+export default [{}];