warning cleanup

src/main/java/carpet/script/exception/ExitStatement.java

@@ -2,12 +2,15 @@ package carpet.script.exception;
 
 import carpet.script.value.Value;
 
+import javax.annotation.Nullable;
+
 /* Exception thrown to terminate execution mid expression (aka return statement) */
 public class ExitStatement extends StacklessRuntimeException
 {
+    @Nullable
     public final Value retval;
 
-    public ExitStatement(final Value value)
+    public ExitStatement(@Nullable Value value)
     {
         retval = value;
     }