MaxScale shutdowns after creating a filter using throttlefilter module without assigning throttling_duration value

The throttling_duration parameter doesn't seem to have default value.

{

    "mandatory": false,

    "name": "throttling_duration",

    "type": "duration",

    "unit": "ms"

},

I received this debug assert printed out:
debug assert at /home/thien/workspace/MaxScale/server/core/config.cc:2288 failed: Invalid value for 'throttling_duration': (rval)