Json_value allows any kind of json value to be stored, not only objects.
type t = json
The type for user-defined contents.
Merge function. Evaluates to
`Conflict msg if the values cannot be merged properly. The arguments of the merge function can take
None to mean that the key does not exists for either the least-common ancestor or one of the two merging points. The merge function returns
None when the key's value should be deleted.