\endinput --> \stop

gefahrgutformular/gefahrgutformular.cls

@@ -21,7 +21,7 @@
   \ClassError{gefahrgutformular}{LuaTeX is required for this class. Aborting.}{%
     This class can only be used with the LuaTeX engine\MessageBreak
     (command `lualatex').}
-  \expandafter\luacode@sty@endinput
+  \expandafter\stop
 \fi
 
 \RequirePackage{fontspec}