Issues with ForeignKey(): IntegrityError at /question/ask/ what is the cause?

Question

Django

Hello, tell me what the problem is, I can’t create a question through the site, the question is created in the admin panel. As far as I understand, the problem is in the database, but I don’t know how to fix it, who can tell me.
here is models.py:

class Question(models.Model):
    title = models.CharField(max_length=120)
    content = models.TextField()
    pub_date = models.DateTimeField(timezone.now)
    author = models.ForeignKey(User)
    views = models.IntegerField(default=0)
    slug = models.SlugField(max_length=240, blank=True)
    tag = TaggableManager()

    def __unicode__(self):
        return self.title

views.py:

def ask(request):
    if request.method == 'POST':
        form = AskForm(request.POST)
        if form.is_valid():
            question = form.save(commit=False)
            question.user = request.user
            question.save()

            return redirect('/question/one_question') + str(question.id)
    return HttpResponseBadRequest()

form.py:

class AskForm(forms.ModelForm):
    tag = forms.CharField(max_length=100, required=False, label='Tags:',
                          help_text="Write here some tags, example: python, django ")

    class Meta:
        model = Question
        fields = ['title', 'content']
        labels = {
            'title': 'Title', 'content': 'Text of your question'
        }

Answer 1

question.user = request.user - what is this user field that is not in the model description?

Answer 2

I did it by example, I just substituted my data, I thought it was a reference to User. changed views to this one:

def ask(request):
    if request.method == 'POST':
        form = AskForm(request.POST)
        if form.is_valid():
            question = form.save(commit=False)
            question.author = request.user
            question.save()

            return redirect('/question/one_question') + str(question.id)
    return HttpResponseBadRequest()

now writes that
question_question.pub_date may not be NULL