Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

Run this:

from rest_framework import serializers

class ChildSerializer(serializers.Serializer):
    id = serializers.IntegerField()

class ParentSerializer(serializers.Serializer):
     ids = ChildSerializer(many=True, allow_empty=False)

serializer = ParentSerializer(data={'ids': []}, partial=True)
serializer.is_valid()

Expected behavior

serializer.is_valid() should return False (as it does when partial=False) because empty values are not allowed.

Actual behavior

It returns True.

I tracked it down to this line and this PR.

I believe it an empty list should not be valid because partial=True is usually about being able to specify a subset of keys. If a value is provided it should still go through the usual validation (in the same way that partial=True does not override allow_null=False).

The documentation for allow_empty does not mention this behaviour either: https://www.django-rest-framework.org/api-guide/serializers/#allow_empty