Problem

Currently, when a schema field is defined as Date and the stored database value of this field is null, DateType Class casts the value a JavaScript Date object representing the Unix epoch (1970-01-01T00:00:00Z).

This behavior causes unintended side effects:

• null values are misrepresented as a valid date.
• Application logic may misinterpret 1970-01-01 as meaningful rather than "no value".

Example:

const doc = await Model.findById(someId);
console.log(doc.dateField); 
// Current behavior → Date("1970-01-01T01:00:00.000Z")
// Expected behavior → null

Proposed Change

Update the DateType.cast() method to return null or undefined as-is, instead of coercing to a Date.

Benefits

• Data integrity: Keeps null values intact, preserving the intent of the stored data.
• Predictability: Matches developer expectations when dealing with optional date fields.
• Backward-compatible: Existing behavior for valid/invalid values remains unchanged.