diff --git a/book_maker/translator/chatgptapi_translator.py b/book_maker/translator/chatgptapi_translator.py
index 5f6f8d3..9b278d5 100644
--- a/book_maker/translator/chatgptapi_translator.py
+++ b/book_maker/translator/chatgptapi_translator.py
@@ -27,7 +27,7 @@ class ChatGPTAPI(Base):
             messages=[
                 {
                     "role": "system",
-                    "content": environ.get("OPENAI_API_SYS_MSG"),
+                    "content": environ.get("OPENAI_API_SYS_MSG") or "",
                 },
                 {
                     "role": "user",