diff --git a/.gitignore b/.gitignore
index 053f1e7..b16afc7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@ config.yaml
 
 # Environment
 .env
+.venv/
 venv/
 
 # Templates
diff --git a/main.py b/main.py
index 1459eb9..69d4c0f 100644
--- a/main.py
+++ b/main.py
@@ -82,13 +82,14 @@ def treat_issues():
                     .filter(project__name__in=action['projects'], status__name__in=action['status'], closed_on=None):
 
                 # Skip issue if start date + time_range is not yet reached
-                if hasattr(issue, 'start_date') \
+                if hasattr(issue, 'start_date') and issue.start_date is not None \
                         and date.today() < (issue.start_date + timedelta(days=+int(action['time_range']))):
                     logging.info(f'Ticket ID: {issue.id}, skipped because start date + time_range not yet reached')
                     continue
 
                 # Skip issue if due date has not yet passed
-                if hasattr(issue, 'due_date') and date.today() < (issue.due_date + timedelta(days=1)):
+                if (hasattr(issue, 'due_date') and issue.due_date is not None
+                        and date.today() < (issue.due_date + timedelta(days=1))):
                     logging.info(f'Ticket ID: {issue.id}, skipped because due date has not yet passed')
                     continue
 
diff --git a/requirements.txt b/requirements.txt
index ff66481..855931a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,11 +1,11 @@
-certifi==2021.5.30
+certifi==2023.7.22
 chardet==4.0.0
 envyaml==1.8.210417
-idna==2.10
-Jinja2==3.0.1
+idna==3.7
+Jinja2==3.1.3
 MarkupSafe==2.0.1
-python-redmine==2.3.0
-PyYAML==5.4.1
-requests==2.25.1
-urllib3==1.26.5
+python-redmine==2.5.0
+PyYAML==6.0.1
+requests==2.31.0
+urllib3==2.0.7
 pytz~=2021.3
\ No newline at end of file