diff --git a/README.md b/README.md
new file mode 100644
index 0000000..76ab166
--- /dev/null
+++ b/README.md
@@ -0,0 +1,20 @@
+# PeeringDB Mirror
+
+This repository implements a simple, Django-based PeeringDB mirroring service
+based on `django-peeringdb` and `peeringdb-py`.
+
+Currently, this doesn't have full PeeringDB API compatibility, but there is a
+sufficiently strong foundation to make that dream easily achievable through a
+bit of Django metaprogramming. PRs welcome!
+
+## Installation
+
+1. Clone this repository: `git clone https://github.com/quantum5/peeringdb-mirror.git`;
+2. Create a virtualenv: `python3 -m venv venv`;
+3. Install dependencies: `pip install -r requirements.txt`;
+4. Configure Django: `cp peeringdb_mirror/settings/{template,local}.py` and edit
+   `peeringdb_mirror/settings/local.py`. You should change `SECRET_KEY` and
+   update `DATABASES`. See the linked Django documentation for details;
+5. Migrate database: `python manage.py migrate`;
+6. Run the WSGI app `peeringdb_mirror.wsgi:application` with your favourite
+   WSGI-capable application server.
diff --git a/peeringdb_api/backend.py b/peeringdb_api/backend.py
index 9b7fcff..528a3b2 100644
--- a/peeringdb_api/backend.py
+++ b/peeringdb_api/backend.py
@@ -13,7 +13,7 @@ class Backend(OldBackend):
         for field in obj._meta.get_fields():
             if isinstance(field, DateTimeField):
                 value = getattr(obj, field.name)
-                if timezone.is_naive(value):
+                if value and timezone.is_naive(value):
                     setattr(obj, field.name, timezone.make_aware(value, utc))
 
         super().clean(obj)