fix(database, update): allow empty objects in ref.update()

As pointed out by @daveGregorian firebase-js-sdk allows empty objects
while the code here was enforcing that the objects had at least one key

Fixes #5218

Author: mikehardy

packages/database/e2e/reference/update.e2e.js

@@ -34,16 +34,6 @@ describe('database().ref().update()', function () {
     }
   });
 
-  it('throws if values does not contain any values', async function () {
-    try {
-      await firebase.database().ref(TEST_PATH).update({});
-      return Promise.reject(new Error('Did not throw an Error.'));
-    } catch (error) {
-      error.message.should.containEql("'values' must be an object containing multiple values");
-      return Promise.resolve();
-    }
-  });
-
   it('throws if update paths are not valid', async function () {
     try {
       await firebase.database().ref(TEST_PATH).update({
@@ -83,6 +73,14 @@ describe('database().ref().update()', function () {
         foo: value,
       }),
     );
+
+    await ref.update({}); // empty update should pass, but no side effects
+    const snapshot2 = await ref.once('value');
+    snapshot2.val().should.eql(
+      jet.contextify({
+        foo: value,
+      }),
+    );
   });
 
   it('callback if function is passed', async function () {

packages/database/lib/DatabaseReference.js

@@ -112,12 +112,6 @@ export default class DatabaseReference extends DatabaseQuery {
       throw new Error("firebase.database().ref().update(*) 'values' must be an object.");
     }
 
-    if (!Object.keys(values).length) {
-      throw new Error(
-        "firebase.database().ref().update(*) 'values' must be an object containing multiple values.",
-      );
-    }
-
     const keys = Object.keys(values);
     for (let i = 0; i < keys.length; i++) {
       if (!isValidPath(keys[i])) {