Apply default value for string form fields if they are empty

cgi-bin/form.py

@@ -172,6 +172,8 @@ def get_form_value(
 			result = cast(form.getfirst(name))
 			if isinstance(result, str):
 				result = result.strip()
+				if not result and default is not None:
+					return default
 			return result
 		except (TypeError, ValueError):
 			fail("400 Bad Request", f"Invalid value for field: {name}")