diff --git a/qc_openscenario/checks/data_type_checker/allowed_operators.py b/qc_openscenario/checks/data_type_checker/allowed_operators.py
index 979fd66..cbb68c2 100644
--- a/qc_openscenario/checks/data_type_checker/allowed_operators.py
+++ b/qc_openscenario/checks/data_type_checker/allowed_operators.py
@@ -1,7 +1,7 @@
 import logging
 
 from dataclasses import dataclass
-from typing import Union
+from typing import Union, Optional
 
 from lxml import etree
 
@@ -47,7 +47,7 @@ class ExpressionMember(enum.IntEnum):
 @dataclass
 class QueueNode:
     element: etree._ElementTree
-    xpath: Union[str, None]
+    xpath: Optional[str]
 
 
 @dataclass
diff --git a/qc_openscenario/checks/models.py b/qc_openscenario/checks/models.py
index aacd3d7..f171f57 100644
--- a/qc_openscenario/checks/models.py
+++ b/qc_openscenario/checks/models.py
@@ -1,6 +1,6 @@
 from dataclasses import dataclass
 from lxml import etree
-from typing import Union
+from typing import Optional
 from enum import Enum
 
 from qc_baselib import Configuration, Result
@@ -9,11 +9,11 @@
 @dataclass
 class CheckerData:
     xml_file_path: str
-    input_file_xml_root: Union[None, etree._ElementTree]
+    input_file_xml_root: Optional[etree._ElementTree]
     config: Configuration
     result: Result
-    schema_version: Union[None, str]
-    xodr_root: Union[None, etree._ElementTree]
+    schema_version: Optional[str]
+    xodr_root: Optional[etree._ElementTree]
 
 
 class AttributeType(Enum):
diff --git a/qc_openscenario/checks/reference_checker/unique_element_names_on_same_level.py b/qc_openscenario/checks/reference_checker/unique_element_names_on_same_level.py
index 99a21e1..95dc937 100644
--- a/qc_openscenario/checks/reference_checker/unique_element_names_on_same_level.py
+++ b/qc_openscenario/checks/reference_checker/unique_element_names_on_same_level.py
@@ -1,14 +1,14 @@
 import logging
 
 from dataclasses import dataclass
-from typing import Union
+from typing import Optional
 
 from lxml import etree
 
-from qc_baselib import IssueSeverity, StatusType
+from qc_baselib import IssueSeverity
 
 from qc_openscenario import constants
-from qc_openscenario.checks import utils, models
+from qc_openscenario.checks import models
 
 from qc_openscenario import basic_preconditions
 from collections import deque, defaultdict
@@ -22,7 +22,7 @@
 @dataclass
 class QueueNode:
     element: etree._ElementTree
-    parent_xpath: Union[str, None]
+    parent_xpath: Optional[str]
 
 
 @dataclass
diff --git a/qc_openscenario/checks/utils.py b/qc_openscenario/checks/utils.py
index a615c24..7d56ce0 100644
--- a/qc_openscenario/checks/utils.py
+++ b/qc_openscenario/checks/utils.py
@@ -1,6 +1,6 @@
 from lxml import etree
 from io import BytesIO
-from typing import Union
+from typing import Union, Optional
 from qc_openscenario.checks import models
 import re
 import logging
@@ -17,7 +17,7 @@ def to_float(s):
         return None
 
 
-def get_root_without_default_namespace(path: str) -> Union[None, etree._ElementTree]:
+def get_root_without_default_namespace(path: str) -> Optional[etree._ElementTree]:
     if not os.path.exists(path):
         return None
 
@@ -30,7 +30,7 @@ def get_root_without_default_namespace(path: str) -> Union[None, etree._ElementT
         return etree.parse(BytesIO(xml_string.encode()))
 
 
-def get_standard_schema_version(root: etree._ElementTree) -> Union[str, None]:
+def get_standard_schema_version(root: etree._ElementTree) -> Optional[str]:
     header = root.find("FileHeader")
     if header is None:
         return None
@@ -107,15 +107,15 @@ def get_parameter_value_from_node(
 
 def get_xodr_road_network(
     input_file_path: str, tree: etree._ElementTree
-) -> Union[etree._ElementTree, None]:
+) -> Optional[etree._ElementTree]:
     """Get parsed xodr tree indicated in the RoadNetwork/LogicFile node of the input tree
 
     Args:
         tree (etree._ElementTree): xml document tree that refers to a xodr file
 
     Returns:
-        Union[etree._ElementTree, None]: the parsed road network tree.
-                                         None if the specified nodes in the root or the road network file are not found
+        Optional[etree._ElementTree]: the parsed road network tree.
+                                      None if the specified nodes in the root or the road network file are not found
     """
 
     road_network = tree.find("RoadNetwork")