diff --git a/sigma/processing/transformations/fields.py b/sigma/processing/transformations/fields.py
index 0cc7b0d4..8d370e45 100644
--- a/sigma/processing/transformations/fields.py
+++ b/sigma/processing/transformations/fields.py
@@ -57,7 +57,7 @@ class FieldPrefixMappingTransformation(FieldMappingTransformation):
     def get_mapping(self, field: str) -> Union[None, str, List[str]]:
         if field is None:
             return None
-        
+
         for src, dest in self.mapping.items():
             if field.startswith(src):  # found matching prefix
                 if isinstance(dest, str):