JSON Merge Patch (RFC 7386)

RFC 6902 is a list of explicit operations — add, remove, replace, move, copy, test — each with a JSON Pointer path, so it can target one array element and it can set a value to null. A merge patch is a document that mirrors the target, so it is much shorter and readable for ordinary field updates, but it cannot address inside an array and cannot set null. Choose 6902 when you need precision, merge patch when you need brevity.

Because that is what the format says: in a merge patch, null means remove this member. There is no escape or alternative spelling. If the value genuinely needs to become null, use RFC 6902 JSON Patch, or have the API accept a sentinel of its own — merge patch has no way to express it.

No. Arrays are replaced whole, so the patch has to carry the complete new array. This is deliberate: merging arrays by position would be ambiguous for anything but the simplest edit, and merging by identity would need the format to know what identity means in your data. If element-level edits matter, RFC 6902 addresses array positions directly.

It replaces the target entirely, whatever the target was. A patch of null produces null, a patch of "bar" produces "bar", and an array patch produces that array. The specification is explicit about it, and this tool warns when the patch is in that shape, because it is almost never what someone sending a PATCH request meant.

No. The specification defines applying a patch, not producing one, so any patch that transforms the source into the target is valid. This tool emits the minimal one: only members whose values differ, plus a null for every member the target dropped. A larger patch that restates unchanged members applies just as correctly.