fix(modules-yaml): don't crash on empty file (#7508)

.changeset/nervous-beds-refuse.md

@@ -0,0 +1,5 @@
+---
+"@pnpm/modules-yaml": patch
+---
+
+readModulesYaml should not crash on empty file.

pkg-manager/modules-yaml/src/index.ts

@@ -38,6 +38,7 @@ export async function readModulesManifest (modulesDir: string): Promise<Modules
   let modules!: Modules
   try {
     modules = await readYamlFile<Modules>(modulesYamlPath)
+    if (!modules) return modules
   } catch (err: any) { // eslint-disable-line
     if ((err as NodeJS.ErrnoException).code !== 'ENOENT') {
       throw err

pkg-manager/modules-yaml/test/index.ts

@@ -113,3 +113,8 @@ test('readModulesManifest() should create a node_modules directory if makeModule
   await writeModulesManifest(modulesDir, modulesYaml, { makeModulesDir: true })
   expect(await readModulesManifest(modulesDir)).toEqual(modulesYaml)
 })
+
+test('readModulesManifest does not fail on empty file', async () => {
+  const modulesYaml = await readModulesManifest(path.join(__dirname, 'fixtures/empty-modules-yaml'))
+  expect(modulesYaml).toBeUndefined()
+})