Erroneous Error: "Cannot create a QWidget without QApplication

#pragma once
#include <QWidget>
class Player : public QWidget
{
    Q_OBJECT
public:
    explicit Player(QWidget *parent = nullptr) : QWidget(parent)
    {
        setAutoFillBackground(false);
        setAttribute(Qt::WA_NoSystemBackground, true);
        setAttribute(Qt::WA_PaintOnScreen, true);
    }
    ~Player() = default;
};

#include <QApplication>
#include "player.h"
int main(int argc, char *argv[]) 
{ 
  QCoreApplication a(argc, argv); 
  Player player; 
  player.show(); 
  return a.exec(); 
}