in lib/src/request.dart [128:138]
set bodyFields(Map<String, String> fields) {
var contentType = _contentType;
if (contentType == null) {
_contentType = MediaType('application', 'x-www-form-urlencoded');
} else if (contentType.mimeType != 'application/x-www-form-urlencoded') {
throw StateError('Cannot set the body fields of a Request with '
'content-type "${contentType.mimeType}".');
}
body = mapToQuery(fields, encoding: encoding);
}