如何使用fetchinreact native上传文件和文本?

我正在尝试使用将文件上载到服务器 react-native-document-picker

unhandled promise rejection unsupported BodyInit type

代码的更新部分

 filepick = () => {
    DocumentPicker.show({
        filetype: [DocumentPickerUtil.images()],
    }, (error, res) => {
        if (error == null) {
            console.log(
                res.uri,
                res.type, // mime type
                res.fileName,
                res.fileSize
            );
            this.setState({
                img_uri: res.uri,
                img_type: res.type,
                img_name: res.fileName

            })
        } else {
            Alert.alert('Message', 'File uploaded failed');
        }
    });
};


 onPressSubmit() {

        const data = new FormData();
        data.append('file', { uri: this.state.img_uri, type: 
       this.state.img_type, name: this.state.img_name })
        data.append('comment', { text: this.state.text });
        AsyncStorage.getItem("userdetail").then(value => {
            fetch(GLOBAL.ASSN_URL +`${this.props.id}`, {
                method: 'POST',
                headers: {
                    'Accept': 'application/json',
                    'Content-Type': 'multipart/form-data',
                    'Authorization': value
                },
                body: data
            }).then((response) => {
                return response.text()
            }).then((responseJson) => {
                var result = responseJson;

                console.log(result);

            });
        })
    }

函数 filepick()