fix(core): handle workspaces set to null (#4039)

Author: merceyz

.yarn/versions/1e028524.yml

@@ -0,0 +1,33 @@
+releases:
+  "@yarnpkg/cli": patch
+  "@yarnpkg/core": patch
+
+declined:
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-essentials"
+  - "@yarnpkg/plugin-exec"
+  - "@yarnpkg/plugin-file"
+  - "@yarnpkg/plugin-git"
+  - "@yarnpkg/plugin-github"
+  - "@yarnpkg/plugin-http"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-link"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/doctor"
+  - "@yarnpkg/nm"
+  - "@yarnpkg/pnpify"
+  - "@yarnpkg/sdks"

packages/yarnpkg-core/sources/Manifest.ts

@@ -410,7 +410,7 @@ export class Manifest {
       }
     }
 
-    if (typeof data.workspaces === `object` && data.workspaces.nohoist)
+    if (typeof data.workspaces === `object` && data.workspaces !== null && data.workspaces.nohoist)
       errors.push(new Error(`'nohoist' is deprecated, please use 'installConfig.hoistingLimits' instead`));
 
     const workspaces = Array.isArray(data.workspaces)

packages/yarnpkg-core/tests/Manifest.test.ts

@@ -6,6 +6,10 @@ describe(`Manifest`, () => {
     expect(manifest.name!.name).toEqual(`foo`);
   });
 
+  it(`should handle 'workspaces' set to null`, () => {
+    expect(() => Manifest.fromText(`{"workspaces":null}`)).not.toThrow();
+  });
+
   describe(`exportTo`, () => {
     it(`should add a scripts field if a script was newly added`, () => {
       const manifest = Manifest.fromText(`{}`);