CombinedCollector tryUnwrap() {
      if (myDownstream instanceof PsiMethodCallExpression call) {
        PsiExpression[] args = call.getArgumentList().getExpressions();
        if (myFinisher == null && isCollectorMethod(call, "collectingAndThen")) {
          return new CombinedCollector(args[0], args[1], myMapper);
        }
        if (myMapper == null && isCollectorMethod(call, "mapping")) {
          return new CombinedCollector(args[1], myFinisher, args[0]);
        }
      }
      return this;
    }
CombinedCollector tryUnwrap()