Merge remote-tracking branch 'origin/master'

src/modules/database/Reference.js

@@ -503,6 +503,14 @@ export default class Reference extends ReferenceBase {
     return `${this._database.databaseUrl}/${this.path}`;
   }
 
+  /**
+   * Return a JSON-serializable representation of this object.
+   * @returns {string}
+   */
+  toJSON(): string {
+    return this.toString();
+  }
+
   /**
    * Returns whether another Reference represent the same location and are from the
    * same instance of firebase.app.App - multiple firebase apps not currently supported.