fixed optinal

src/rag.py

@@ -155,7 +155,7 @@ class AICompletion:
         self.human = "{text}"
         self.model = ChatOpenAI(model=chat_model, temperature=temperature)
 
-    def get_answer(self, system_prompt: str, text: str) -> (str | None):
+    def get_answer(self, system_prompt: str, text: str) -> Optional[str]:
         prompt = ChatPromptTemplate.from_messages([("system", system_prompt),
                                                    ("human", self.human)])
         chain = prompt | self.model