[Python] wtforms: optional FieldList of IntegerField?

I need an optional list of int's in a WTForms-validated Rest API.

Right now this is the relevant part of my form:

from wtforms import IntegerField, FileField, StringField, FieldList
from wtforms.validators import DataRequired, Optional, UUID

class PublishForm(FlaskForm):
# This validates, but the patch_bases list comes up empty.
# patch_bases = FieldList(IntegerField("pb", validators=[Required()]), min_entries=0, max_entries=5, validators=[Optional()])
# This too.
patch_bases = FieldList(IntegerField(), min_entries=0, max_entries=5, validators=[Optional()])


Here's the call to validate/parse:

form = PublishForm()
if not form.validate_on_submit():
return form_error_response(form.errors)


And here's (part of) a test curl I'm using to hit the API:

curl \
-v \
-X POST \
-H "Authorization: Bearer $(set -eu; cat token)" \
--form 'patch_bases=[2, 4]' \
http://hostname:8080/api/v3/publish


I'm using --form because I need to upload a file as well (not shown here).

I'm consistently getting back a "successfully validated" empty list even when I pass a nonempty list of int's via curl, which is not what I want.

What I want, ideally, is a None for no patch_bases field specified at all, an empty list for patch_bases=[], or a nonempty list for 1 to 5 int's in patch_bases - all in form.patch_bases.data.

I've Googled about this extensively on more than one occasion, but I'm not seeing a way of doing what I want.

I'm using:

WTForms 2.0.2
Python 3.10.12


I know, the WTForms version is ancient, but I'm stuck with it for now unless there's a pretty compelling reason to upgrade.

If there's a fine manual to read, feel free to point me at it? I dug around in the WTForms 2.3.x doc on Fields (among many other Google hits), but didn't see what I need.

Thanks!

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