Disable timerserver when timerserver-interval is 0.

Also, make it optional.

stack/erp5/buildout.cfg

@@ -230,7 +230,7 @@ mode = 640
 [template-zope-conf]
 recipe = slapos.recipe.build:download
 url = ${:_profile_base_location_}/zope.conf.in
-md5sum = 599e004c18fd3461aa846ae75bd112f2
+md5sum = bc2154161a1d5baddc4ed4dfaaf94fbe
 mode = 640
 
 [template]

stack/erp5/zope.conf.in

@@ -43,10 +43,11 @@ products {{ instance_products }}
 </product-config>
 
 {% endif -%}
-{% if 'timerserver-interval' in parameter_dict -%}
+{% set timerserver_interval = parameter_dict.get('timerserver-interval', '0') | int -%}
+{% if timerserver_interval -%}
 %import timerserver
 <timer-server>
-  interval {{ parameter_dict['timerserver-interval'] }}
+  interval {{ timerserver_interval }}
 </timer-server>
 
 {% endif -%}