Error on upgrading to new config file version

[mlookaxw]

For configuration files in the old format having fields with "property" attribute set to null, the field will not be upgraded to the newer version.

Example:

"fields": {
  "attributeValue#0": {
    "property": null, 
    "type": "string", 
    "used": true, 
    "value": "artifact"
  }
}

This results in the error message:
ERROR: ValueError(u"Missing 'source' property in field 'xxxxxx' of entity 'xxxxxx'",)

[mlookaxw]

Issue fixed with release v0.11.2