Added test cases for fix

Author: rhodgkins

spec/v1/providers/database.spec.ts

@@ -454,6 +454,13 @@ describe("DataSnapshot", () => {
       expect(subject.child("a").val()).to.deep.equal({ b: "c", d: "e" });
     });
 
+    it("should return null for null data", () => {
+      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;
+    });
+
     it("should return null for children past a leaf", () => {
       populate(applyChange({ a: 23 }, { b: 33 }));
       expect(subject.child("a/b").val()).to.be.null;
@@ -466,6 +473,8 @@ describe("DataSnapshot", () => {
       expect(subject.val()).to.eq(23);
       populate({ b: 23, a: null });
       expect(subject.child("b").val()).to.eq(23);
+      expect(subject.child("a").val()).to.be.null;
+      expect(subject.child("a/c").val()).to.be.null;
     });
 
     it("should coerce object into array if all keys are integers", () => {