null value in column “ProjectName_id” violates not-null constraint

[Robb Rodirguez Jr.]

Hello need help on null value in column "ProjectName_id" violates not-null constraint, im new to django

i want my ProjectName_id (Foreignkey) is the same/equal id that user choose in my majordetails = ProjectNameInviToBid.objects.get(id=sid) please help me...

my model views

class ProjectNameInviToBid(models.Model):
    ProjectName = models.CharField(max_length=255, verbose_name='Project Name', null=True)
    DateCreated = models.DateField(auto_now=True)

class InviToBid(models.Model):
    today = date.today()
    ProjectName = models.ForeignKey('ProjectNameInviToBid', on_delete=models.CASCADE)
    NameOfFile = models.CharField(max_length=255, verbose_name='Name of File')

my views.py
def project_name_details(request, sid):

    majordetails = ProjectNameInviToBid.objects.get(id=sid)

    if request.method == 'POST':
        form = invitoBidForm(request.POST, request.FILES)
        if form.is_valid():
            majordetails = InviToBid.ProjectName
            form.save()
            messages.success(request, 'File has been Uploaded')
    else:
        form = invitoBidForm()

    args = {
        'majordetails': majordetails,
        'form': form

    }
    return render(request,'content/invitoBid/bacadmininvitoBid.html', args)