Auto-calculation of ExpirationActionDate & MaturityDate when creating lot via REST API In Fusion

We are using the following REST API to create an inventory lot:
/fscmRestApi/resources/11.13.18.05/inventoryItemLots

Request Payload:
{
"OrganizationCode": "WA002",
"ItemNumber": "310015",
"LotNumber": "1012423503-300635149",
"OriginationDate": "2024-08-22",
"ExpirationDate": "2026-08-22",
"StatusCode": "TRANSFORM",
"OriginationType": "Other",
"Grade": "103",
"MaturityDate": null,
"ExpirationActionDate": null
}

The lot is getting created successfully;
however, even though we are passing MaturityDate and ExpirationActionDate as null, the system is automatically populating both fields with calculated values.

Queries / Clarifications Requested:

1. How are the values for ExpirationActionDate and MaturityDate being derived automatically when they are passed as null?
2. Are these values being calculated based on any setup in the Item Master?
3. Is there a way to prevent these fields from being auto-calculated when explicitly passed as null through the REST API?