Erro ao clicar no botão

O ERRO:

I/flutter (19144): Clicou no btn salvar

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════ The following StackOverflowError was thrown while handling a gesture: Stack Overflow

When the exception was thrown, this was the stack:

#0 StringBase.interpolate (dart:core-patch/string_patch.dart:835:3)

#1 Transferencia.toString (package:byte_bank/modelos/Transferencia.dart:12:70)

#2 StringBase.interpolate (dart:core-patch/string_patch.dart:842:19)

#3 Transferencia.toString (package:byte_bank/modelos/Transferencia.dart:12:70)

#4 StringBase.interpolate (dart:core-patch/string_patch.dart:842:19) ... Handler: "onTap" Recognizer: TapGestureRecognizer#f7d3c debugOwner: GestureDetector state: possible won arena finalPosition: Offset(152.3, 272.0) finalLocalPosition: Offset(29.8, 26.0) button: 1 sent tap down ═════════════════════════════════════════════

E O CÓDIGO :

Widget botaoSalvarTransferencia() {
    return RaisedButton(
      child: Text(
        "Salvar",
        style: TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
      ),
      color: Colors.blueAccent,
      textColor: Colors.white,
      padding: const EdgeInsets.fromLTRB(32, 16, 32, 16),
      shape: RoundedRectangleBorder(
        borderRadius: new BorderRadius.circular(8.0),
      ),
      onPressed: () {
        print("Clicou no btn salvar");
        final double valor = double.tryParse(_controladorValor.text);
        final int numeroDaConta = int.tryParse(_controladorNumeroConta.text);
        if (numeroDaConta != null && valor != null) {
          final transferencia = Transferencia(valor, numeroDaConta);
          debugPrint('$transferencia');
        }
      },
    );
  }