Add support for QueryDict data in serializers.ListField

[chank1012]

Failing case:

When user uploads multiple images (for example, <input type="file" name="image_files" multiple="">) and I try to serialize it with:

• image_files = serializers.ListField(child=serializers.FileField(write_only=True))

Serializer fails to evaluate "list of files".

Problem:
https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/fields.py#L1273

    # Suppose dictionary.__class__ == QueryDict
    def get_value(self, dictionary):
        # dictionary has attribute 'getlist', so is_html_input returns True
        if html.is_html_input(dictionary):
            # but try to parse it as MultiDict
            return html.parse_html_list(dictionary, prefix=self.field_name)
        return dictionary.get(self.field_name, empty)

ListField class doesn't handle QueryDict-typed data properly.

Solution:

I haven't looked up for all codes related to this issue, so my PR is just a naive hotfix. I think there should be more consistent method to handle both QueryDict & MultiDict data types.

[tomchristie]

Now resolved - thanks for the report! Upcoming in the latest 3.1.4 release.