diff --git a/api/serialization/util/__init__.py b/api/serialization/util/__init__.py
index 6bdcd95..0b182a9 100644
--- a/api/serialization/util/__init__.py
+++ b/api/serialization/util/__init__.py
@@ -50,7 +50,9 @@ def instance_to_model(instance: Any, * , use_class: Type=None, skip_classes: Lis
     
     if instance is None:
         return None
-    if isinstance(instance, (str, int, float)):
+    if isinstance(instance, str):
+        return instance
+    if isinstance(instance, (int, float)):
         if math.isnan(instance):
             return None
         return instance
diff --git a/test/serialization/test_util.py b/test/serialization/test_util.py
new file mode 100644
index 0000000..0a73604
--- /dev/null
+++ b/test/serialization/test_util.py
@@ -0,0 +1,24 @@
+import pytest
+import math
+
+from api.serialization.util import instance_to_model
+
+@pytest.mark.parametrize("target, result, error", [
+    (None, None, None),
+    ("foo", "foo", None),
+    (1, 1, None),
+    (0.1, 0.1, None),
+    (math.nan, None, None),
+    ([1, 2], [1, 2], None),
+    ((1, 2), [1, 2], None),
+    ({"foo": "bar", "one": 2}, {"foo": "bar", "one": 2}, None),
+    ({"foo": [1, "bar"]}, {"foo": [1, "bar"]}, None),
+    ({"foo": (1, "bar")}, {"foo": [1, "bar"]}, None),
+])
+def test_instance_to_model(target, result, error):
+    if error:
+        with pytest.raises(error):
+            instance_to_model(target)
+            pass
+        return
+    assert result == instance_to_model(target)