Fix crash if SHIELDS_IO_BASE_URL is undefined

validata_ui/config.py

@@ -26,5 +26,5 @@ else:
 
 
 SHIELDS_IO_BASE_URL = os.environ.get("SHIELDS_IO_BASE_URL") or None
-if not SHIELDS_IO_BASE_URL.endswith('/'):
+if SHIELDS_IO_BASE_URL and not SHIELDS_IO_BASE_URL.endswith('/'):
     SHIELDS_IO_BASE_URL += '/'