multipartStringFile method
Implementation
MethodWithBody multipartStringFile(String field, String? value,
{String? filename, MediaType? contentType}) {
if (_body is! Map<String, Multipart>) {
_body = <String, Multipart>{};
}
if (value != null) {
_body[field] = MultipartStringFile(value,
filename: filename, contentType: contentType);
}
return this;
}