Add filter_fields to extras.ObjectVar & fix default value handling

Author: thatmattlove

netbox/extras/scripts.py

@@ -181,16 +181,19 @@ class ObjectVar(ScriptVariable):
 
     :param model: The NetBox model being referenced
     :param query_params: A dictionary of additional query parameters to attach when making REST API requests (optional)
+    :param filter_fields: A dictionary or list of dictionaries that define a related
+        field. Example: `{'accessor': 'group_id', 'field_name': 'tenant_group'}` (optional)
     :param null_option: The label to use as a "null" selection option (optional)
     """
     form_field = DynamicModelChoiceField
 
-    def __init__(self, model, query_params=None, null_option=None, *args, **kwargs):
+    def __init__(self, model, query_params=None, filter_fields=None, null_option=None, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
         self.field_attrs.update({
             'queryset': model.objects.all(),
             'query_params': query_params,
+            'filter_fields': filter_fields,
             'null_option': null_option,
         })
 

netbox/utilities/forms/fields.py

@@ -416,7 +416,7 @@ def widget_attrs(self, widget):
             widget.add_query_param(key, value)
 
         # Attach any dynamic query parameters
-        if len(self.filter_fields) > 0:
+        if self.filter_fields is not None and len(self.filter_fields) > 0:
             widget.add_filter_fields(self.filter_fields)
 
         return attrs