Fixes access on deeply nested, nonexistent property (#1432)

* return null on nonexistent deeply nested property

* update changelog

* check specifically for undefined in val()

* fix lint issue

---------

Co-authored-by: Cole Rogers <colerogers@users.noreply.github.com>

Author: blidd-google

CHANGELOG.md

@@ -0,0 +1 @@
+- Fixes access on deeply nested, nonexistent property. (#1432)

spec/v1/providers/database.spec.ts

@@ -458,6 +458,7 @@ describe("DataSnapshot", () => {
       populate(applyChange({ a: 23 }, { b: 33 }));
       expect(subject.child("a/b").val()).to.be.null;
       expect(subject.child("b/c").val()).to.be.null;
+      expect(subject.child("a/b/c").val()).to.be.null;
     });
 
     it("should return a leaf value", () => {

src/common/providers/database.ts

@@ -120,6 +120,9 @@ export class DataSnapshot implements database.DataSnapshot {
     let source = this._data;
     if (parts.length) {
       for (const part of parts) {
+        if (source[part] === undefined) {
+          return null;
+        }
         source = source[part];
       }
     }