City is no more required at the database level. Refs #51

db/migrate/20160111124855_modify_city_nullable.rb

+# Events and orgas do not require a city anymore
+class ModifyCityNullable < ActiveRecord::Migration
+  def change
+    change_column :events, :city, :string, default: '', null: true
+    change_column :orgas, :city, :string, default: '', null: true
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160109203136) do
+ActiveRecord::Schema.define(version: 20160111124855) do
 
   create_table "active_admin_comments", force: :cascade do |t|
     t.string   "namespace",     limit: 255
@@ -63,7 +63,7 @@ ActiveRecord::Schema.define(version: 20160109203136) do
     t.text     "description",       limit: 65535,              null: false
     t.datetime "start_time",                                   null: false
     t.datetime "end_time",                                     null: false
-    t.string   "city",              limit: 255,   default: "", null: false
+    t.string   "city",              limit: 255,   default: ""
     t.integer  "region_id",         limit: 4,     default: 0,  null: false
     t.integer  "locality",          limit: 4,     default: 0,  null: false
     t.string   "url",               limit: 255,   default: "", null: false
@@ -104,7 +104,7 @@ ActiveRecord::Schema.define(version: 20160109203136) do
     t.string   "department",      limit: 4,   default: "0",   null: false
     t.string   "name",            limit: 255, default: "",    null: false
     t.string   "url",             limit: 255, default: "",    null: false
-    t.string   "city",            limit: 255, default: "",    null: false
+    t.string   "city",            limit: 255, default: ""
     t.integer  "kind_id",         limit: 4
     t.string   "feed",            limit: 255
     t.string   "contact",         limit: 255