fixed dependency

vertex_ai_service.py

@@ -59,15 +59,13 @@ class VertexAIService(ImageProcessingInterface):
             # Authenticate using the file
             creds = service_account.Credentials.from_service_account_file(self.json_key_path)
         else:
-            # Get JSON key from environment variable
-            json_key = os.getenv(self.json_key_env_var)
 
-            if not json_key:
-                raise ValueError(f"Environment variable {self.json_key_env_var} is not set.")
+            if not self.json_key_env_var:
+                raise ValueError(f"Environment variable {json_key_env_var} is not set.")
 
             # Save JSON key to a temporary file
             with tempfile.NamedTemporaryFile(delete=False) as temp_file:
-                temp_file.write(json_key.encode('utf-8'))
+                temp_file.write(self.json_key_env_var.encode('utf-8'))
                 temp_file_path = temp_file.name
 
             # Create credentials object