diff --git a/fgmetric/metric.py b/fgmetric/metric.py
index f06c809..35f5543 100644
--- a/fgmetric/metric.py
+++ b/fgmetric/metric.py
@@ -82,6 +82,8 @@ def _empty_field_to_none(cls, data: Any) -> Any:
             # short circuit
             return data
 
+        data = dict(data)
+
         for field, value in data.items():
             info = cls.model_fields.get(field)
             if info is None: