How to get the foreign key value into href attribute of a hyperlink element as a url parameter in Django template

I have data table showing list of vehicles from the Vehicle model with Driver column. When user clicking on the Driver column value, I want to redirect the user to driver detail page url driver-detail/license_number.I tried to pass the license_number to href attribute of hyperlink element like href="{% url 'driver-detail' vehicle.driver.license_number %}". This does not help me, it's always empty. If I omit the license_number in the href value it will pass the __str__(self) return value of the Driver model, which is combination of license_number and fullname. If I change the return value of __str__(self) in the Driver model it will work. But I don't want to change the return value of __str__(self).Any help is much appreciated!

Model.py

class Driver(models.Model):    license_number = models.CharField(primary_key=True, max_length=50)    fullname = models.CharField(max_length=25)    license_issue_date = models.DateField("Issued Date")    def __str__(self):        return self.license_number +" " + self.fullnameclass Vehicle(models.Model):    license_plate = models.CharField(max_length=25, primary_key=True)    model = models.CharField(max_length=100, verbose_name="Vehicle model")        driver = models.ForeignKey(Driver,on_delete=models.SET_NULL,null=True, blank=True)    

template.html

<a href="{% url 'driver-detail' vehicle.driver.license_number %}" >    {{vehicle.driver.license_number}}{{vehicle.driver.fullname}}</a>

urls.py

urlpatterns = [    path('driver-detail/<str:pk>/', views.driverDetail, name='driver-detail'),]