Script generating empty JSON schemas for some YANG models

[rwestphal]

Hi,

First of all, thanks for writing this very interesting piece of software.

I'm opening this issue because this script is generating empty JSON schemas for some YANG models like ietf-mpls.yang. Other YANG models like ietf-interfaces.yang and ietf-routing.yang are converted just fine:

renato@renato-pc ~/yang/pyang-json-schema-plugin/ldp $ ls
ietf-inet-types.yang  ietf-interfaces.yang  [email protected]  ietf-mpls.yang  ietf-routing-types.yang  ietf-routing.yang  ietf-yang-types.yang

renato@renato-pc ~/yang/pyang-json-schema-plugin/ldp $ pyang --plugindir ../ -f json-schema ./ietf-routing.yang
...lots of output...

renato@renato-pc ~/yang/pyang-json-schema-plugin/ldp $ pyang --plugindir ../ -f json-schema ./ietf-mpls.yang 
{
  "$schema": "http://json-schema.org/draft-04/schema#", 
  "type": "object", 
  "description": "Generated by pyang from module ietf-mpls", 
  "properties": {}, 
  "title": "ietf-mpls"
}

Any idea of what might be causing this? I tried to use --json-schema-debug but it didn't provide any useful information.