Fixed issue calling DataSnapshot methods with null data (#1661)

* Fixed issue calling DataSnapshot methods with null data (see firebase/firebase-functions-test#254)

* Added test cases for fix

* Better fix for calling DataSnapshot#val() with null data

* Add changelog.

---------

Co-authored-by: Daniel Lee <danielylee@google.com>
Co-authored-by: Daniel Lee <taeold@gmail.com>

Author: rhodgkins

CHANGELOG.md

@@ -1,3 +1,4 @@
 - Add LLM guidance (#1736)
+- Fix issue calling DataSnapshot methods with null data (#1661)
 - Adds auth.rawToken to context to allow access to the underlying token. (#1678)
 - Fix logger runtime exceptions #(1704)

spec/v1/providers/database.spec.ts

@@ -494,20 +494,31 @@ describe("DataSnapshot", () => {
     it("should deal with null-values appropriately", () => {
       populate(null);
       expect(subject.val()).to.be.null;
+      expect(subject.child("a").val()).to.be.null;
+      expect(subject.child("a/b").val()).to.be.null;
 
       populate({ myKey: null });
       expect(subject.val()).to.be.null;
+      expect(subject.child("myKey").val()).to.be.null;
+      expect(subject.child("myKey/a").val()).to.be.null;
+      expect(subject.child("myKey/a/b").val()).to.be.null;
+      expect(subject.child("a").val()).to.be.null;
+      expect(subject.child("a/b").val()).to.be.null;
     });
 
     it("should deal with empty object values appropriately", () => {
       populate({});
       expect(subject.val()).to.be.null;
+      expect(subject.child("a").val()).to.be.null;
 
       populate({ myKey: {} });
       expect(subject.val()).to.be.null;
+      expect(subject.child("myKey").val()).to.be.null;
 
       populate({ myKey: { child: null } });
       expect(subject.val()).to.be.null;
+      expect(subject.child("myKey").val()).to.be.null;
+      expect(subject.child("myKey/child").val()).to.be.null;
     });
 
     it("should deal with empty array values appropriately", () => {

src/common/providers/database.ts

@@ -131,7 +131,7 @@ export class DataSnapshot implements database.DataSnapshot {
     }
     if (parts.length) {
       for (const part of parts) {
-        if (source[part] === undefined) {
+        if (typeof source === "undefined" || source === null) {
           return null;
         }
         source = source[part];