diff --git a/forms-flow-api/src/formsflow_api/resources/form_process_mapper.py b/forms-flow-api/src/formsflow_api/resources/form_process_mapper.py
index e82dd1c743..f948de772f 100644
--- a/forms-flow-api/src/formsflow_api/resources/form_process_mapper.py
+++ b/forms-flow-api/src/formsflow_api/resources/form_process_mapper.py
@@ -22,6 +22,8 @@
 
 
 class NullableString(fields.String):
+    """Extending String field to be nullable."""
+
     __schema_type__ = ["string", "null"]
     __schema_example__ = "nullable string"