Почему вылезает ошибка валидности?

forms.py:
class Postform(forms.ModelForm):
    class Meta:
        model=Post
        fields=['title','sometext','tags']
        widgets={
            'title':forms.TextInput(attrs={'class':'form-control'}),
            'tags': forms.SelectMultiple(attrs={'class': 'form-control'}),
            'sometext':forms.Textarea(attrs={'class':'form-control'})
        }<code lang="django">

</code>

    def clean_title(self):
        new_text = self.cleaned_data['title'].lower
        if new_text =='':
            raise ValidationError('title may not be')
        if Post.objects.filter(title__iexact=new_text).count():
            raise ValidationError('title must be unique We have it"{}" it yet'.format(new_text))
        return new_text
    def save(self):
        new_post=Post.objects.create(title=self.cleaned_data['title'],
                                     sometext=self.cleaned_data['sometext'],
                                     tags=self.cleaned_data['tags'],
                                     )
        return new_post
html формы:
{% extends 'foundation/base.html' %}
{% block title %}
    Create Post - {{block.super}}
{% endblock %}


{% block content %}
    <form action="{% url 'postcreate_url' %}" method="post" >
        {% csrf_token %}
        {% for field in form %}
            <div class="form-group">
                {{ field.label}}
                {{ field}}
            </div>
            {% if field.errors %}
                <div class="alert alert-danger">
                    {{ field.errors}}
                </div>
            {% endif %}
        {% endfor %}
        <button type="submit" class="btn btn-primary" >Create Post</button>
    </form>
{% endblock %}
views.py:
class Postcreate(View):
    def get(self,request):
        form =Postform()
        return render(request,'foundation/Post_create.html',context={'form':form})
    def post(self,request):
        bound_form=Postform(request.POST)
        print(bound_form)
        print(bound_form['title'])
        if bound_form.is_valid():
            new_post=bound_form.save()
            return redirect(new_post)
        return render(request, 'foundation/Post_create.html', context={'form': bound_form})

models.py:
from django.db import models
from django.shortcuts import reverse

# Create your models here.
class Post(models.Model):
    title = models.CharField(max_length=50, db_index=True)
    sometext=models.CharField(max_length=50,db_index=True)
    tags=models.ManyToManyField('Tag',blank=True, related_name='posts')
    date_pub=models.DateTimeField(auto_now_add=True)
    def __str__(self):
        return self.title
    def get_absolute_url(self):
        return reverse('postdetail_url',kwargs={'sometext':self.sometext})
		

class Tag(models.Model):
    title=models.CharField(max_length=50)
    sometext=models.CharField(max_length=50)
    def get_absolute_url(self):
        return reverse('tag_url',kwargs={'title':self.title})

    def _str_(self):
        return self.title