SharedPreferences: fix None handling

internal_filesystem/lib/mpos/config.py

@@ -172,7 +172,7 @@ class Editor:
 
     def put_string(self, key, value):
         """Store a string value."""
-        self.temp_data[key] = str(value)
+        self.temp_data[key] = None if value is None else str(value)
         return self
 
     def put_int(self, key, value):

tests/test_shared_preferences.py

@@ -432,6 +432,14 @@ class TestSharedPreferences(unittest.TestCase):
         # Getting a nonexistent key should return None or default
         self.assertIsNone(prefs.get_string("nonexistent"))
 
+    def test_put_string_none_value(self):
+        """Test that putting None stores and returns a real None."""
+        prefs = SharedPreferences(self.test_app_name)
+        prefs.edit().put_string("auto_start_app_early", None).commit()
+
+        prefs2 = SharedPreferences(self.test_app_name)
+        self.assertIsNone(prefs2.get_string("auto_start_app_early"))
+
     def test_special_characters_in_keys(self):
         """Test keys with special characters."""
         prefs = SharedPreferences(self.test_app_name)