define landing page fix

app.py

@@ -154,7 +154,7 @@ def ref_parse_book(ref):
 @app.get("/define")
 def define():
     ref = request.args.get("kw", None)
-    ref = ref.strip()
+    if ref: ref = ref.strip()
     if not ref:
         return send_file("html/dictionary.html")
     with open(dictionary_json, 'r') as data: