Flutter Error: Unsupported operation: Platform._version on web

I use packages http: ^ 0.12.2

this is my iport

import 'package: http / http.dart' as http;
import 'dart: io';
import 'dart: convert';

for retrieving the data from a server. It works fine with Android and iOS. But on the web I get the error message Unsupported operation: Platform._version

this is my function:

Future getUserData() async {
    var url_ = "${APIDomain}/antragsteller/1";
      HttpClient client = new HttpClient();
      client.badCertificateCallback =
          ((X509Certificate cert, String host, int port) => true);

      HttpClientRequest request = await client.getUrl(Uri.parse(url_));
      request.headers.set('content-type', 'application/json');
      request.headers.set('Access-Control-Allow-Origin', '*');
      HttpClientResponse response = await request.close();

      String reply = await response.transform(utf8.decoder).join();
      this.userData = jsonDecode(reply);
  }

the return value is then of course empty. My internet search did not produce any useful results. Can someone please help me find the cause and solve the problem. Thank you!