Option to fill in zero bytes for fixed size data types when undefined?

Oh, sorry about custom type it is just an example, I think this should be an option for any type that can have a count set to a fixed number.

If you have a definition with a fixed size.

{
  "name": "foo",
  "type": [
    "fcstring",
    {
      "count": 4,
      "trim": true
    }
  ]
}

And wanted to serialize some object where it is undefined
{}

Then the buffer should zero fill.

<Buffer 00 00 00 00>

Example with buffer data type.

{
  "name": "foo",
  "type": [
    "buffer",
    {
      "count": 4
    }
  ]
}

<Buffer 00 00 00 00>

And applicable to arrays as well.

Would such an option be possible?
Maybe when setting up the serializer.

Start by locating the serializer setup and the handling for fixed-count types. Add coverage for undefined fixed-size fcstring and buffer values, including arrays, and verify that serialization produces the requested zero-filled buffers. The issue does not name specific files or tests, so repository exploration is required.