writeJsonString handles undefined in an array in a wrong way.

[pavel]

file source/vibe/data/json.d

writeJsonString function (line 1537) is handling undefined inside array by skipping it, see line 1555. This ruins one of the array's invariants, which is order.

Suppose, if in some system you expect [name, surname, address], then even if surname is undefined or null, you should get ["Mike", null, "Some street"] and not ["Mike", "Some street"].

JSON.stringify description by Mozilla:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify (section description, 3rd point)