Fix bug where onCall handler failed to encode returned value that contained a function (#1000)

In #915, we replaced use of `_.isObject(data)` with `typeof data === 'object'`. 

Turns out that `_.isObject` returns `true` for functions ([code](https://github.com/lodash/lodash/blob/2da024c3b4f9947a48517639de7560457cd4ec6c/isObject.js#L26)). We update the condition to match the previous behavior.

Fixes #964

Author: taeold

CHANGELOG.md

@@ -1,3 +1,4 @@
 - GCS Enhancement
-- Add option to allow callable functions to ignore invalid App Check tokens.
+- Add option to allow callable functions to ignore invalid App Check tokens
 - Add firebase-admin v10 as an allowed peer dependency
+- Fix bug where onCall handler failed to encode returned value with functions

spec/common/providers/https.spec.ts

@@ -665,4 +665,8 @@ describe('encoding/decoding', () => {
       baz: [1, 2, 1099511627776],
     });
   });
+
+  it('encodes function as an empty object', () => {
+    expect(https.encode(() => 'foo')).to.deep.equal({});
+  });
 });

src/common/providers/https.ts

@@ -426,7 +426,7 @@ export function encode(data: any): any {
   if (Array.isArray(data)) {
     return data.map(encode);
   }
-  if (typeof data === 'object') {
+  if (typeof data === 'object' || typeof data === 'function') {
     // Sadly we don't have Object.fromEntries in Node 10, so we can't use a single
     // list comprehension
     const obj: Record<string, any> = {};