allow null category id

app.py

@@ -169,7 +169,7 @@ def route_admin_songs_id_post(id):
         else:
             output['courses'][course] = None
     
-    output['category_id'] = int(request.form.get('category_id'))
+    output['category_id'] = int(request.form.get('category_id')) or None
     output['type'] = request.form.get('type')
     output['offset'] = float(request.form.get('offset')) or None
     output['skin_id'] = int(request.form.get('skin_id')) or None

templates/admin_song_detail.html

@@ -65,6 +65,7 @@
         <div class="form-field">
             <p><label for="category_id">Category</label></p>
             <select name="category_id" id="category_id">
+                <option value="0">(none)</option>
                 {% for category in categories %}
                     <option value="{{ category.id }}"{% if song.category_id == category.id %} selected{% endif %}>{{ category.title }}</option>
                 {% endfor %}