fix(toolkit): correcty load cdk.json file without context (#1900)

Author: rix0rrr

packages/aws-cdk/lib/settings.ts

@@ -86,8 +86,8 @@ export class Context {
   }
 
   public everything(): {[key: string]: any} {
-    const b = this.bottom.get(this.bottomPrefixPath);
-    const t = this.top.get([]);
+    const b = this.bottom.get(this.bottomPrefixPath) || {};
+    const t = this.top.get([]) || {};
     return Object.assign(b, t);
   }
 

packages/aws-cdk/test/test.context.ts

@@ -110,4 +110,36 @@ export = {
 
     test.done();
   },
+
+  async 'surive missing new file'(test: Test) {
+    // GIVEN
+    await fs.writeJSON('cdk.json', { context: { boo: 'far' } });
+    const config = await new Configuration().load();
+
+    // WHEN
+    test.deepEqual(config.context.everything(), { boo: 'far' });
+    await config.saveContext();
+
+    // THEN
+    test.deepEqual(await fs.readJSON('cdk.context.json'), {});
+    test.deepEqual(await fs.readJSON('cdk.json'), { context: { boo: 'far' } });
+
+    test.done();
+  },
+
+  async 'surive no context in old file'(test: Test) {
+    // GIVEN
+    await fs.writeJSON('cdk.json', { });
+    await fs.writeJSON('cdk.context.json', { boo: 'far' });
+    const config = await new Configuration().load();
+
+    // WHEN
+    test.deepEqual(config.context.everything(), { boo: 'far' });
+    await config.saveContext();
+
+    // THEN
+    test.deepEqual(await fs.readJSON('cdk.context.json'), { boo: 'far' });
+
+    test.done();
+  },
 };