diff --git a/src/documents/serialisers.py b/src/documents/serialisers.py
index 510aaa244..36387d586 100644
--- a/src/documents/serialisers.py
+++ b/src/documents/serialisers.py
@@ -529,6 +529,10 @@ class CustomFieldInstanceSerializer(serializers.ModelSerializer):
         """
         Add or remove 'symmetrical' links to `document` on all `target_doc_ids`
         """
+
+        if target_doc_ids is None:
+            target_doc_ids = []
+
         # Check if any documents are going to be removed from the current list of links and remove the symmetrical links
         current_field_instance = CustomFieldInstance.objects.filter(
             field=field,
@@ -542,9 +546,6 @@ class CustomFieldInstanceSerializer(serializers.ModelSerializer):
                 if doc_id not in target_doc_ids:
                     self.remove_doclink(document, field, doc_id)
 
-        if target_doc_ids is None:
-            target_doc_ids = []
-
         # Create an instance if target doc doesnt have this field or append it to an existing one
         existing_custom_field_instances = {
             custom_field.document_id: custom_field