diff --git a/src/database/api/Query.ts b/src/database/api/Query.ts
index aec0d6770e0..4b9e66fec3b 100644
--- a/src/database/api/Query.ts
+++ b/src/database/api/Query.ts
@@ -22,6 +22,10 @@ import { DataSnapshot } from './DataSnapshot';
 
 let __referenceConstructor: new(repo: Repo, path: Path) => Query;
 
+export interface SnapshotCallback {
+  (a: DataSnapshot, b?: string): any
+}
+
 /**
  * A Query represents a filter to be applied to a firebase location.  This object purely represents the
  * query expression (and exposes our public API to build the query).  The actual query logic is in ViewBase.js.
@@ -143,8 +147,8 @@ export class Query {
    * @param {Object=} context
    * @return {!function(DataSnapshot, string=)}
    */
-  on(eventType: string, callback: (a: DataSnapshot, b?: string) => any,
-     cancelCallbackOrContext?: ((a: Error) => any) | Object, context?: Object): (a: DataSnapshot, b?: string) => any {
+  on(eventType: string, callback: SnapshotCallback,
+     cancelCallbackOrContext?: ((a: Error) => any) | Object, context?: Object): SnapshotCallback {
     validateArgCount('Query.on', 2, 4, arguments.length);
     validateEventType('Query.on', 1, eventType, false);
     validateCallback('Query.on', 2, callback, false);
@@ -177,7 +181,7 @@ export class Query {
    * @param {?function(Error)} cancelCallback
    * @param {?Object} context
    */
-  onChildEvent(callbacks: { [k: string]: (a: DataSnapshot, b: string | null) => any },
+  onChildEvent(callbacks: { [k: string]: SnapshotCallback },
                cancelCallback: ((a: Error) => any) | null, context: Object | null) {
     const container = new ChildEventRegistration(callbacks, cancelCallback, context);
     this.repo.addEventCallbackForQuery(this, container);
@@ -217,7 +221,7 @@ export class Query {
    * @param context
    * @return {!firebase.Promise}
    */
-  once(eventType: string, userCallback: (a: DataSnapshot, b?: string) => any,
+  once(eventType: string, userCallback: SnapshotCallback,
        cancelOrContext?, context?: Object) {
     validateArgCount('Query.once', 1, 4, arguments.length);
     validateEventType('Query.once', 1, eventType, false);
@@ -376,7 +380,7 @@ export class Query {
     }
 
     // Calling with no params tells us to start at the beginning.
-    if (value == null) {
+    if (value === undefined) {
       value = null;
       name = null;
     }
diff --git a/tests/config/project.json b/tests/config/project.json
new file mode 100644
index 00000000000..10dc41ebbbc
--- /dev/null
+++ b/tests/config/project.json
@@ -0,0 +1 @@
+{"apiKey":"AIzaSyBNHCyZ-bpv-WA-HpXTmigJm2aq3z1kaH8","authDomain":"jscore-sandbox-141b5.firebaseapp.com","databaseURL":"https://jscore-sandbox-141b5.firebaseio.com","projectId":"jscore-sandbox-141b5","storageBucket":"jscore-sandbox-141b5.appspot.com","messagingSenderId":"280127633210"}