Error Flutter (186)] Unhandled Exception: FormatException: Unexpected character (at character 1)

I got this problem

***> E/flutter (15532): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)]

Unhandled Exception: FormatException: Unexpected character (at character 1) E/flutter (15532):
E/flutter (15532): ^ E/flutter (15532): E/flutter (15532): #0 _ChunkedJsonParser.fail (dart:convert-patch/convert_patch.dart:1404:5) E/flutter (15532): #1
_ChunkedJsonParser.parseNumber (dart:convert-patch/convert_patch.dart:1271:9) E/flutter (15532): #2
_ChunkedJsonParser.parse (dart:convert-patch/convert_patch.dart:936:22) E/flutter (15532): #3
_parseJson (dart:convert-patch/convert_patch.dart:40:10) E/flutter (15532): #4 JsonDecoder.convert (dart:convert/json.dart:506:36) E/flutter (15532): #5 JsonCodec.decode (dart:convert/json.dart:157:41) E/flutter (15532): #6 jsonDecode (dart:convert/json.dart:96:10) E/flutter (15532): #7
_LoginState.login (package:flutter_login/main.dart:35:18) E/flutter (15532): E/flutter (15532):***

this is my code

    void main() {
  HttpOverrides.global = new MyHttpOverrides();
  runApp(MaterialApp(
    home: login(),
  ));
}

class login extends StatefulWidget {
  @override
  _LoginState createState() => _LoginState();
}

class _LoginState extends State<login>{
  var email,password;
  final _key = new GlobalKey<FormState>();
  check(){
    final form = _key.currentState;
    if(form.validate()){
      form.save();
      login();
    }
  }

  login() async{
    final response = await http.post(Uri.parse("link"),
        body: {
      "email" : email,
      "password" : password
    });
    final data = jsonDecode(response.body);
    print(data);
  }

  bool _secureText = false;
  showHide(){
    setState(() {
      _secureText = !_secureText;
    });
  }

can help me? pls