Fix codegen for Null at top level in alternative transformation

src/main/java/org/sablecc/sablecc/GenerateAlternativeCodeForParser.java

@@ -124,19 +124,22 @@ public class GenerateAlternativeCodeForParser extends DepthFirstAdapter
 
         position = CG.getTermNumbers().get(term);
 
-        if(type_name.startsWith("L"))
+        if("null".equals(type_name))
         {
-          type_name = "list";
+          macros.apply(file, "ParserNewBodyListAddNull", null);
         }
-        else if(type_name.equals("null"))
+        else
         {
-          type_name = "null";
+          if(type_name.startsWith("L"))
+          {
+            type_name = "list";
           }
           else
           {
             type_name = type_name.toLowerCase();
           }
           macros.apply(file, "ParserNewBodyListAdd", new String[] {type_name, "" + position});
+        }
 
       }
       if (popCount > 0) {

src/main/resources/org/sablecc/sablecc/parser.txt

@@ -390,6 +390,11 @@ Macro:ParserNewBodyListAdd
 
 $
 
+Macro:ParserNewBodyListAddNull
+        nodeList.add(null);
+
+$
+
 Macro:ParserNewCheck
         checkResult(nodeList.get(0), nodeArrayList1, nodeArrayList$0$);