Issue regarding null values

[nickydonna]

We have an issue with an special merger. We need to keep the properties even if the source object has that property as undefined, so we use a custom merger, with almost all values they work ok, but when the original object has a value of null, the resulting property is set to undefined.

const Immutable = require("seamless-immutable").static;

const merger = (c, o) => {
    if (o === undefined && c !== undefined) {
      return c;
    }
    return;
}

Immutable.merge({a: 1}, {a: undefined}, {merger}) // {a: 1}
Immutable.merge({a: null}, {a: undefined}, {merger}) // {a: undefined}

Here is the code running on runkit https://runkit.com/donnanicolas/seamless-immutable-null

We don't know why this happens

[crudh]

Seems like a problem in the addToResult function in the merge function:

seamless-immutable/src/seamless-immutable.js

Line 405 in 281c344

if (mergerResult) {

So if the result from the merger is not truthy it will go to the else and use the value from o. It should do an explicit check for undefined instead. But I guess a fix for that would require a new major version since it can break stuff.

[nickydonna]

@crudh Ok, but it seem like a major issue, since anyone using null values can have issues like this and its rather hard to track

[crudh]

@donnanicolas yeah, I agree. PR #248 should fix it.

[nickydonna]

@crudh Thanks!! will update as soon as the PR is merged!! (I "reviewed" it and it seems great, but I don't know much about the code)

[crudh]

This is fixed now, a release will be done soon.