Standard Required Fields (e.g., Case Status) Accept Null Values via Apex or API Due to the defaultedOnCreate Metadata Settingg

Some standard required fields in Salesforce — such as the Status field on the Case object — can be set to null when updated via Apex or the Salesforce API, without triggering a validation error. This is unexpected because the fields are marked as required in the Salesforce UI.

The reason this behavior occurs is a metadata-level interaction between two field properties: nillable and defaultedOnCreate.

• nillable: true means the field accepts null values programmatically, even if it is required in the UI.
• defaultedOnCreate: true means the field receives a default value at record creation time and will never be null after initial insert.

When a field has defaultedOnCreate: true, Salesforce may mark it as nillable: true, because the system guarantees a default value exists at creation. This combination overrides the required constraint at the programmatic level, allowing null values to be set via Apex DML or API calls without throwing an exception.
This behavior differs from fields on objects like Order, where both nillable and defaultedOnCreate are set in a way that strictly enforces the required constraint at all levels