Send null as id using a custom exporter with fetchRelatedRecord and nullable ids

[Luwangel]

We have a list of ids and we want to use fetchRelatedRecords method in a custom Exporter. Theses ids could be null.

const data = [1, 2, 3, null, null, 1, 7, null];

What you were expecting:

The api request should be:

http://example.com/react-admin/table?id[]=1&id[]=2&id[]=3&id[]=7

What happened instead:

The api request is:

http://example.com/react-admin/table?id[]=null&id[]=1&id[]=2&id[]=3&id[]=7

Steps to reproduce:

Pre-Conditions:

• Have a table containing foreign nullable keys

For example user_category_id is a foreign nullable key:

{
    users: [
        {
            id: 1,
            name: "Logan Schowalter",
            role: "admin",
            user_category_id: null
        },
        {
            id: 2,
            name: "Breanna Gibson",
            role: "user",
            user_category_id: 1
        },
    ],
    user_categories: [
        {
            id: 1,
            label: "premium"
        },
    ]
}

Steps:

1. Create a custom export of users list
2. Use fetchRelatedRecords to retrieve user_category label

Related code:

https://codesandbox.io/s/p1k5vol6x

Environment

• React-admin version: 2.3.x
• React version: 16.4.x

[fzaninotto]

Fixed by #2354