Reading QR code crashes iOS(Objective C) application

I have created one React Native application for barcode/QRCode scanning functionality. I used third party barcode scanner library.I am able to scan barcode properly, but application getting crashed on QR code scan.Here is sample code:

- (void)captureOutput:(AVCaptureOutput *)output didOutputMetadataObjects:(NSArray<__kindof AVMetadataObject *> *)metadataObjects fromConnection:(AVCaptureConnection *)connection{ for (AVMetadataObject *object in metadataObjects) {  if ([object isKindOfClass:[AVMetadataMachineReadableCodeObject class]]) {    if (_callback != nil) {        _callback(@{                    @"format": object.type,                    @"content": [(AVMetadataMachineReadableCodeObject *)object stringValue]                    });    }}

}}

it returns nil when I am trying scan QR code and application is getting crash on this line

[(AVMetadataMachineReadableCodeObject *)object stringValue] 

and getting exception error is

-[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[0]