Fixes #7808: Fix reference values for content type under custom field import form

Author: jeremystretch

docs/release-notes/version-3.0.md

@@ -20,6 +20,7 @@
 * [#7788](https://github.com/netbox-community/netbox/issues/7788) - Improve XSS mitigation in Markdown renderer
 * [#7791](https://github.com/netbox-community/netbox/issues/7791) - Enable sorting device bays table by installed device status
 * [#7802](https://github.com/netbox-community/netbox/issues/7802) - Differentiate ID and VID columns in VLANs table
+* [#7808](https://github.com/netbox-community/netbox/issues/7808) - Fix reference values for content type under custom field import form
 * [#7809](https://github.com/netbox-community/netbox/issues/7809) - Add missing export template support for various models
 
 ---

netbox/utilities/forms/fields.py

@@ -304,7 +304,7 @@ def prepare_value(self, value):
                 app_label, model = name.split('.')
                 ct_filter |= Q(app_label=app_label, model=model)
             return list(ContentType.objects.filter(ct_filter).values_list('pk', flat=True))
-        return super().prepare_value(value)
+        return f'{value.app_label}.{value.model}'
 
 
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