diff --git a/modules/openapi-generator/src/main/resources/python-flask/util.mustache b/modules/openapi-generator/src/main/resources/python-flask/util.mustache
index f2b90009a46..60ebebac8e1 100644
--- a/modules/openapi-generator/src/main/resources/python-flask/util.mustache
+++ b/modules/openapi-generator/src/main/resources/python-flask/util.mustache
@@ -67,6 +67,9 @@ def deserialize_date(string):
     :return: date.
     :rtype: date
     """
+    if string is None:
+      return None
+    
     try:
         from dateutil.parser import parse
         return parse(string).date()
@@ -84,6 +87,9 @@ def deserialize_datetime(string):
     :return: datetime.
     :rtype: datetime
     """
+    if string is None:
+      return None
+    
     try:
         from dateutil.parser import parse
         return parse(string)
diff --git a/samples/server/petstore/python-flask/openapi_server/util.py b/samples/server/petstore/python-flask/openapi_server/util.py
index e1185a713ec..2a63f2109ba 100644
--- a/samples/server/petstore/python-flask/openapi_server/util.py
+++ b/samples/server/petstore/python-flask/openapi_server/util.py
@@ -67,6 +67,9 @@ def deserialize_date(string):
     :return: date.
     :rtype: date
     """
+    if string is None:
+      return None
+    
     try:
         from dateutil.parser import parse
         return parse(string).date()
@@ -84,6 +87,9 @@ def deserialize_datetime(string):
     :return: datetime.
     :rtype: datetime
     """
+    if string is None:
+      return None
+    
     try:
         from dateutil.parser import parse
         return parse(string)