Why is this ModelForm not valid - django

Question

I'm new to coding with django, and I'm trying to add comments to my blog app, but I'm having trouble with the validation of this form, it always returns False with form.is_valid(), so the object is never saved
views.py
def blog_post_detail_view(request, slug):
obj = get_object_or_404(BlogPost, slug=slug)
comments = Comment.objects.filter(blog_post=obj)
initial_data = {
"blog_post": obj,
}
form = CommentModelForm(request.POST or None, initial=initial_data)
if form.is_valid():
comment_obj = form.save(commit=False)
comment_obj.user = request.user
comment_obj.save()
form = CommentModelForm()
else:
print('not clean')
context = {
"object": obj,
"comments": comments,
"form": form,
}
template_name = 'blog/detail.html'
return render(request, template_name, context)
forms.py
from django import forms
from .models import Comment
class CommentModelForm(forms.ModelForm):
class Meta:
model = Comment
fields = ['content','blog_post']
HTML
<form method='POST' action='.'> {% csrf_token %}
{{ form.as_p }}
<button type='submit'>Send</button>
</form>
models.py
class Comment(models.Model):
content = models.TextField(max_length=300)
user = models.ForeignKey(User, null=True, on_delete=models.SET_NULL, default=1)
blog_post = models.ForeignKey(BlogPost, null=True, on_delete=models.CASCADE)
timestamp = models.DateTimeField(auto_now_add=True)
def __unicode__(self):
return str(self.user.username)
def __str__(self):
return str(self.user.username)