diff --git a/src/agenda_culturel/models.py b/src/agenda_culturel/models.py
index 27dd471..104a126 100644
--- a/src/agenda_culturel/models.py
+++ b/src/agenda_culturel/models.py
@@ -11,6 +11,10 @@ from datetime import datetime
 
 class Category(models.Model):
 
+    default_name = "Sans catégorie"
+    default_css_class = "cat-nocat"
+    default_color = "#aaaaaa"
+
     COLOR_PALETTE = [
         ("#ea5545", "color 1"),
         ("#f46a9b", "color 2"),
@@ -103,7 +107,8 @@ class Event(models.Model):
         tags = list(Event.objects.values_list('tags', flat = True))
         uniq_tags = set()
         for t in tags:
-            uniq_tags = uniq_tags | set(t)
+            if t is not None:
+                uniq_tags = uniq_tags | set(t)
         return list(uniq_tags)
 
 
diff --git a/src/agenda_culturel/templatetags/cat_extra.py b/src/agenda_culturel/templatetags/cat_extra.py
index 08ce5ad..08b618b 100644
--- a/src/agenda_culturel/templatetags/cat_extra.py
+++ b/src/agenda_culturel/templatetags/cat_extra.py
@@ -60,24 +60,25 @@ def background_color_adjust_color(color, alpha = 1):
 def css_categories():
     result = '<style type="text/css">'
     
-    cats = Category.objects.all()
+    cats = [{"color": c.color, "css_class": c.css_class()} for c in Category.objects.all()]
+    cats.append({"color": Category.default_color, "css_class": Category.default_css_class})
 
     for c in cats:
 
-        result += "." + c.css_class() + " {"
-        result += background_color_adjust_color(adjust_lightness_saturation(c.color, .2, 0.8), 0.8)
+        result += "." + c["css_class"] + " {"
+        result += background_color_adjust_color(adjust_lightness_saturation(c["color"], .2, 0.8), 0.8)
         result += "}"
 
-        result += "*:hover ." + c.css_class() + " {"
-        result += background_color_adjust_color(adjust_lightness_saturation(c.color, 0.02, 1.0))
+        result += "*:hover ." + c["css_class"] + " {"
+        result += background_color_adjust_color(adjust_lightness_saturation(c["color"], 0.02, 1.0))
         result += "}"
         
-        result += ".selected ." + c.css_class() + " {"
-        result += background_color_adjust_color(c.color)
+        result += ".selected ." + c["css_class"] + " {"
+        result += background_color_adjust_color(c["color"])
         result += "}"
 
-        result += "a.selected:hover ." + c.css_class() + " {"
-        result += background_color_adjust_color(adjust_lightness_saturation(c.color, 0.2, 1.2))
+        result += "a.selected:hover ." + c["css_class"] + " {"
+        result += background_color_adjust_color(adjust_lightness_saturation(c["color"], 0.2, 1.2))
         result += "}"
 
     result += '</style>'
@@ -86,12 +87,18 @@ def css_categories():
 @register.filter
 def small_cat(category, url=None, contrast=True):
 
+    name = Category.default_name if category is None else category.name
+    css_class = Category.default_css_class if category is None else category.css_class()
+
     class_contrast = " contrast" if contrast else ""
     if url is None:
-        return mark_safe('<span class="small-cat' + class_contrast +' selected" role="button"><span class="cat ' + category.css_class() + '"></span> ' + category.name + "</span>")
+        return mark_safe('<span class="small-cat' + class_contrast +' selected" role="button"><span class="cat ' + css_class + '"></span> ' + name + "</span>")
     else:
-        return mark_safe('<a class="small-cat' + class_contrast +' selected" role="button" href="' + url + '"><span class="cat ' + category.css_class() + '"></span> ' + category.name + "</a>")
+        return mark_safe('<a class="small-cat' + class_contrast +' selected" role="button" href="' + url + '"><span class="cat ' + css_class + '"></span> ' + name + "</a>")
 
 @register.filter
 def circle_cat(category):
-    return mark_safe('<span class="cat ' + category.css_class() + '" data-tooltip="' + category.name + '"></span>')
\ No newline at end of file
+    if category is None:
+        return mark_safe('<span class="cat ' + Category.default_css_class + '" data-tooltip="' + Category.default_name + '"></span>')
+    else:
+        return mark_safe('<span class="cat ' + category.css_class() + '" data-tooltip="' + category.name + '"></span>')
\ No newline at end of file
diff --git a/src/agenda_culturel/views.py b/src/agenda_culturel/views.py
index 85865d0..97e4f2c 100644
--- a/src/agenda_culturel/views.py
+++ b/src/agenda_culturel/views.py
@@ -52,9 +52,14 @@ class CalendarDay:
 
     def add_event(self, event):
         self.events.append(event)
-        if not event.category.name in self.events_by_category:
-            self.events_by_category[event.category.name] = []
-        self.events_by_category[event.category.name].append(event)
+        if event.category is None:
+            if not "" in self.events_by_category:
+                self.events_by_category[""] = []
+            self.events_by_category[""].append(event)
+        else:
+            if not event.category.name in self.events_by_category:
+                self.events_by_category[event.category.name] = []
+            self.events_by_category[event.category.name].append(event)
 
 
 class CalendarList: