fixes

src/yamlhttpforms/form.py

@@ -28,6 +28,8 @@ class FormField:
             for attr in function.split('.'):
                 obj = getattr(obj, attr)
             self._default = obj
+        elif default is None:
+            self._default = None
         else:
             self._default = str(default)
         self.options: Optional[OptionsT] = None