The field session can be marked as private.

h2/src/main/org/h2/table/TableFilter.java

@@ -39,7 +39,7 @@ public class TableFilter implements ColumnResolver {
 
     private static final int BEFORE_FIRST = 0, FOUND = 1, AFTER_LAST = 2, NULL_ROW = 3;
 
-    protected Session session;
+    private Session session;
 
     /**
      * Whether this is a direct or indirect (nested) outer join