Small fixes to get started

- docker-compose needs the flag --build to (re)build all containers
- Initially, on an empty database, Track.aggregate returns an empty array,
  which results in an undefined error for /api/stats

README.md

@@ -9,7 +9,16 @@ separated into components:
 * **frontend**: A React single-page application that allows access to the data,
   provides summaries and visualizations, and lets users adjust settings and
   manage and publish their tracks.
-  
+
+## Clone the Project
+
+First of all, you must clone this project. This project uses submodules,
+thus ensure, that they are cloned as well:
+
+```bash
+git submodule update --init --recursive
+```
+
 ## Deployment setup
 
 You should be familiar with managing a Linux server. If not, find a suitable
@@ -48,7 +57,7 @@ Compose](https://docs.docker.com/compose/install/) onto your machine, and
 cloning the repository, all you need to do is:
 
 ```bash
-docker-compose up -d
+docker-compose up -d --build
 ```
 
 If this does not work, please open an issue and describe the problem you're

api/src/routes/api/stats.js

@@ -14,7 +14,7 @@ router.get(
     const publicTrackCount = await Track.find({ public: true }).count();
     const userCount = await User.find().count();
 
-    const [{ trackLength, numEvents, trackDuration }] = await Track.aggregate([
+    const aggregateResult = await Track.aggregate([
       {
         $addFields: {
           trackLength: '$statistics.length',
@@ -39,6 +39,8 @@ router.get(
       },
     ]);
 
+    const [trackLength, numEvents, trackDuration] = aggregateResult.length > 0 ? aggregateResult : [0,0,0];
+
     const trackLengthPrivatized = Math.floor(trackLength / TRACK_LENGTH_ROUNDING) * TRACK_LENGTH_ROUNDING;
 
     return res.json({