Treat Empty String as NULL in JSON Reader

In the JSON below the field `resolved_by` first appears as a map but in records when it is not defined, is empty strings.  This causes SchemaChangeExceptions. 

I'm wondering if Drill could either ignore or interpret the empty strings as null so that the query will complete.

{{{
....
  "skills": "",
      "number": "INC0000001",
      "resolved_by": {
        "link": "https://empmgill4.service-now.com/api/now/table/sys_user/6816f79cc0a8016401c5a33be04be441",
        "value": "6816f79cc0a8016401c5a33be04be441"
      },
      "sys_updated_by": "admin"
...
},

{       ...       "number": "INC0000002",       "resolved_by": "",       "sys_updated_by": "admin", ... }}

}