Optional DateTimeField doesn't accept an empty string as a falsey value

[marksweb]

This must have been asked before, but I can't find it. I've got a DateTimeField on a model that's allowed to be blank/null. Now I'm adding this to a serializer to allow for data loading from CSV;

class EventLoader(serializers.ModelSerializer):

    release_time = serializers.DateTimeField(allow_null=True, required=False)

An empty field in a CSV comes through as an empty string, rather than None, so the test data being fed into the serializer looks like this;

            {
                "name": "Game 2",
                "release_time": "2024-02-08 20:00:00+00:00",
            },
            {
                "name": "Game 3",
                "release_time": "",
            },

The code this then hits (here) doesn't check for an empty string and throws;

MySerializer failed with validation errors: ", {'release_time': [ErrorDetail(string='Datetime has wrong format. Use one of these formats instead:

The subclass for null values is fairly simple;

class NullDateTimeField(serializers.DateTimeField):
    """
    The default DateTimeField does not allow null values, so this one does.
    """

    NULL_VALUES = ["", "None", None]

    def to_internal_value(self, data):
        """
        This value here is checked for null values, and if it is one,
        then returns. The default class expects any string, empty of not,
        to be a valid value.
        """
        if data in self.NULL_VALUES:
            return None
        return super().to_internal_value(data)