Standardize empty value on report.json

[davidgamez]

Describe the problem

The report.json generated by the validator contains the string "N/A" for a few fields when no data is associated with it. On the consumer side, this is "hard" to process as "N/A" is not a standard for empty values, and also, in our own report.json, is not standardized across all string fields.

Example:

{
  "summary": {
    "validatorVersion": "6.0.0",
    "validatedAt": "2025-03-05T14:56:45Z",
    "gtfsInput": "file:/tmp/gtfs-validator-temp1125035072567570096/7ba835bd-a78b-4e80-9fcc-7dac689bbb336306016345572776134.zip",
    "threads": 1,
    "outputDirectory": "/tmp/gtfs-validator-temp7ba835bd-a78b-4e80-9fcc-7dac689bbb336893178565669548670",
    "systemErrorsReportName": "system_errors.json",
    "validationReportName": "report.json",
    "htmlReportName": "report.html",
    "countryCode": "ZZ",
    "dateForValidation": "2025-03-05",
    "feedInfo": {
      "publisherName": "N/A",
      "publisherUrl": "N/A",
      "feedLanguage": "N/A",
      "feedEmail": "N/A",
      "feedServiceWindowStart": "",
      "feedServiceWindowEnd": ""
    },

Proposed solution

In case of empty values, use the following rule:

• For string fields,the empty string ""
• For other field types, null

Update the HTML report to make sure the N/A is not part of the rendering logic.

Alternatives you've considered

No response

Additional context

No response