It's impossible to create the kit unpack list

When I was reviewing OLMIS-6212, I noticed that currently, it's impossible to create the kit unpack list. When trying to do so, errors in the console occur, as visible on screenshots. The issue occurs on both browsers.

Whole error from Network:

{
"timestamp" : "2020-09-30T06:32:25.443+0000",
"status" : 400,
"error" : "Bad Request",
"message" : "JSON parse error: null; nested exception is com.fasterxml.jackson.databind.JsonMappingException: N/A\n at [Source: (PushbackInputStream); line: 1, column: 544] (through reference chain: org.openlmis.referencedata.dto.OrderableDto["children"]->java.util.HashSet[0]->org.openlmis.referencedata.dto.OrderableChildDto["orderable"]->org.openlmis.referencedata.domain.Orderable["id"])",
"path" : "/api/orderables/d602d0c6-4052-456c-8ccd-61b4ad77bece"
}

Reproduction steps:

1. Log in as administrator.

2. Go to Administration > Products.

3. Click the “Edit” button next to any product.

4. Go to the “Kit Unpack List” tab.

5. Click the “Add Product” button.

6. Select any product and click the “Add Products” button.

7. Enter any number in the “Quantity” field and click the “Save Kit Unpack List” button.

8. The list is not created. Instead, errors occur.

Expected results:

• It should be possible to create kit unpack lists;

• It should be possible to update kit unpack lists (including deletion).