Attempt to reduce JSON output size using the "omitempty" marshaling directive

[mrutkows]

See if we can take LicenseChoice objects produced in the license list command (JSON format):

{
      "license": {
          "id": "BSD-3-Clause",
          "name": "",
          "text": {
              "contentType": "",
              "encoding": "",
              "content": ""
          },
          "url": ""
      },
      "expression": ""
},

and reduce them to:

{
        "license": {
            "id": "BSD-3-Clause"
        }
},