handle errors and fix join form

config/application.rb

@@ -12,6 +12,8 @@ module Greenlight20
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.
 
+    config.exceptions_app = self.routes
+
     config.loadbalanced_configuration = (ENV["USE_LOADBALANCED_CONFIGURATION"] == "true")
 
     # Setup BigBlueButton configuration.
@@ -33,4 +35,4 @@ module Greenlight20
     # Determine if GreenLight should allow non-omniauth signup/login.
     config.greenlight_accounts = (ENV['ALLOW_GREENLIGHT_ACCOUNTS'] == "true")
   end
-end
+end