diff --git a/integrations/google-vertex/pyproject.toml b/integrations/google-vertex/pyproject.toml
index a34853a60..8a5e2a7db 100644
--- a/integrations/google-vertex/pyproject.toml
+++ b/integrations/google-vertex/pyproject.toml
@@ -157,6 +157,7 @@ exclude_lines = [
 
 [[tool.mypy.overrides]]
 module = [
+  "google.*",
   "vertexai.*",
   "haystack.*",
   "pytest.*",
diff --git a/integrations/google-vertex/src/google_vertex_haystack/generators/utils.py b/integrations/google-vertex/src/google_vertex_haystack/generators/utils.py
index 3fcfd3ee0..124340136 100644
--- a/integrations/google-vertex/src/google_vertex_haystack/generators/utils.py
+++ b/integrations/google-vertex/src/google_vertex_haystack/generators/utils.py
@@ -1,10 +1,11 @@
 import os
+from typing import Optional
 
 import vertexai
 from google.auth.api_key import Credentials
 
 
-def authenticate(api_key: str = "", project_id: str = "", location: str = ""):
+def authenticate(api_key: str = "", project_id: str = "", location: Optional[str] = None):
     """
     Authenticates using the provided API key, project ID, and location.