docs: void collectRangeVariables(RangeVariable[] rangeVariables, Set set) {
  
          for (int i = 0; i < nodes.length; i++) {
              if (nodes[i] != null) {
                  nodes[i].collectRangeVariables(rangeVariables, set);
              }
          }
  
          if (subQuery != null && subQuery.queryExpression != null) {
              HsqlList unresolvedExpressions =
                  subQuery.queryExpression.getUnresolvedExpressions();
  
              if (unresolvedExpressions != null) {
                  for (int i = 0; i < unresolvedExpressions.size(); i++) {
                      Expression e = (Expression) unresolvedExpressions.get(i);
  
                      e.collectRangeVariables(rangeVariables, set);
                  }
              }
          }
      }