code: protected Criterion addToCriteria(Criterion c) {
          if (!logicalExpressionStack.isEmpty()) {
              logicalExpressionStack.get(logicalExpressionStack.size() - 1).args.add(c);
          }
          else {
              criteria.add(c);
          }
          return c;
      }
docs: adds and returns the given criterion to the currently active criteria set.
  this might be either the root criteria or a currently open
  LogicalExpression.