From 0f0010bac0855e146f21522be94fa9148d7220e3 Mon Sep 17 00:00:00 2001
From: Daniel Sheppard <dans@dansheps.com>
Date: Wed, 27 Jan 2021 09:21:00 -0600
Subject: [PATCH] Fixes: #5315 - Make "null_option" on DynamicModelChoiceField
 also null the value on the model.

---
 docs/release-notes/version-2.10.md | 8 ++++++++
 netbox/utilities/forms/fields.py   | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/docs/release-notes/version-2.10.md b/docs/release-notes/version-2.10.md
index b6bc33229..f5e0b4fa2 100644
--- a/docs/release-notes/version-2.10.md
+++ b/docs/release-notes/version-2.10.md
@@ -1,5 +1,13 @@
 # NetBox v2.10
 
+## v2.10.5 (FUTURE)
+
+### Bug Fixes
+
+* [#5315](https://github.com/netbox-community/netbox/issues/5315) - Fix site unassignment from VLAN when using "None" option
+
+---
+
 ## v2.10.4 (2021-01-26)
 
 ### Enhancements
diff --git a/netbox/utilities/forms/fields.py b/netbox/utilities/forms/fields.py
index a5b76fd8d..3cf421213 100644
--- a/netbox/utilities/forms/fields.py
+++ b/netbox/utilities/forms/fields.py
@@ -355,7 +355,11 @@ class DynamicModelChoiceField(DynamicModelChoiceMixin, forms.ModelChoiceField):
     Override get_bound_field() to avoid pre-populating field choices with a SQL query. The field will be
     rendered only with choices set via bound data. Choices are populated on-demand via the APISelect widget.
     """
-    pass
+
+    def clean(self, value):
+        if self.null_option is not None and value == 'null':
+            return None
+        return super().clean(value)
 
 
 class DynamicModelMultipleChoiceField(DynamicModelChoiceMixin, forms.ModelMultipleChoiceField):