diff --git a/lib/config/presets/__snapshots__/local.spec.ts.snap b/lib/config/presets/__snapshots__/local.spec.ts.snap
index 8cbbc16a2444f6fae184771a7bcad70b111f9476..f2713740ee5bcb36f2eec6c1fdfae85e1877e59a 100644
--- a/lib/config/presets/__snapshots__/local.spec.ts.snap
+++ b/lib/config/presets/__snapshots__/local.spec.ts.snap
@@ -42,7 +42,7 @@ exports[`config/presets/local getPreset() forwards to github 1`] = `
 Array [
   Array [
     "some/repo",
-    "",
+    "default",
     Object {
       "platform": "github",
     },
diff --git a/lib/config/presets/local.spec.ts b/lib/config/presets/local.spec.ts
index 0c7a22f59fe8464b6cf80b81615241355cc6961c..affa203bf2d0ba6a14ea78909436617f4f3bf373 100644
--- a/lib/config/presets/local.spec.ts
+++ b/lib/config/presets/local.spec.ts
@@ -42,7 +42,7 @@ describe('config/presets/local', () => {
     });
 
     it('forwards to github', async () => {
-      const content = await local.getPreset('some/repo', '', {
+      const content = await local.getPreset('some/repo', undefined, {
         platform: 'github',
       });
       expect(githubGetPreset.mock.calls).toMatchSnapshot();
diff --git a/lib/manager/npm/post-update/yarn.ts b/lib/manager/npm/post-update/yarn.ts
index a54b80b7e94021e87ff1d367738a4706e7b52e4e..f2dfc7b5acb845511caa857d74c496592fe30fd6 100644
--- a/lib/manager/npm/post-update/yarn.ts
+++ b/lib/manager/npm/post-update/yarn.ts
@@ -126,12 +126,9 @@ export async function generateLockFile(
         cwd,
         env,
       });
-      stdout += updateRes.stdout
-        ? /* istanbul ignore next */ updateRes.stdout
-        : '';
-      stderr += updateRes.stderr
-        ? /* istanbul ignore next */ updateRes.stderr
-        : '';
+      // istanbul ignore next
+      stdout += updateRes.stdout || '';
+      stderr += updateRes.stderr || '';
     }
 
     if (yarnMajorVersion < 2) {
@@ -146,12 +143,9 @@ export async function generateLockFile(
           cwd,
           env,
         });
-        stdout += dedupeRes.stdout
-          ? /* istanbul ignore next */ dedupeRes.stdout
-          : '';
-        stderr += dedupeRes.stderr
-          ? /* istanbul ignore next */ dedupeRes.stderr
-          : '';
+        // istanbul ignore next
+        stdout += dedupeRes.stdout || '';
+        stderr += dedupeRes.stderr || '';
       }
       if (
         config.postUpdateOptions &&
@@ -164,17 +158,13 @@ export async function generateLockFile(
           cwd,
           env,
         });
-        stdout += dedupeRes.stdout
-          ? /* istanbul ignore next */ dedupeRes.stdout
-          : '';
-        stderr += dedupeRes.stderr
-          ? /* istanbul ignore next */ dedupeRes.stderr
-          : '';
+        // istanbul ignore next
+        stdout += dedupeRes.stdout || '';
+        stderr += dedupeRes.stderr || '';
       }
     } else if (
       config.postUpdateOptions &&
-      (config.postUpdateOptions.includes('yarnDedupeFewer') ||
-        config.postUpdateOptions.includes('yarnDedupeHighest'))
+      config.postUpdateOptions.some((option) => option.startsWith('yarnDedupe'))
     ) {
       logger.warn('yarn-deduplicate is not supported since yarn 2');
     }