isFsfLibre field not always present in JSON files

[dheurtev]

Issue

• In the licenses.json file, the field "isFsfLibre" can be true, false, but if not present, the field is not present instead of being left blank
• per the relevant section of the license-fields.md file of the XML license list

F) FSF Free/Libre?
If the license is [listed as free by the FSF](https://www.gnu.org/licenses/license-list.en.html), this field will indicate "Y". If the license is listed as not free by the FSF, the field will indicate "N". Otherwise, the field will be left blank.

• To ease parsing, it would be best to normalize the data to always include the isFsfLibre field in the JSON output.

Proposed Solution

• Best : always include the isFsfLibre field.
• Potential : document that the FSF Free/Libre field is optional in json files.

[goneall]

Just to confirm the proposal:

• If the license is listed free by the FSF: "isFsfLibre": true
• If the license is listed as not free by the FSF: "isFsfLibre": false
• If the license is not listed: "isFsfLibre": null

[dheurtev]

Correct. It would be then consistent with the wording in the XML documentation.

[goneall]

In looking into a fix, it looks like the library we use (Gson) has an option to serialize nulls for all properties, but it doesn't look like you can chose this for individual properties (it is an option in the builder).

There are several other nullable fields, I'm not sure we should include all of them.