A continuación se muestran mis modelos. Sigo recibiendo un error cuando python manage.py migrate

 django.db.utils.IntegrityError: NOT NULL constraint failed: app_project.description

Modelos dados a continuación:

 from django.db import models # Create your models here. class Project(models.Model): title = models.CharField(max_length=100) description = models.TextField(max_length=2000, blank=True, default='') progress = models.FloatField(default=0) created_at = models.DateTimeField(auto_now_add=True) updated_at = models.DateTimeField(auto_now=True) def __str__(self): return self.title class Task(models.Model): project = models.ForeignKey(Project, on_delete=models.CASCADE) title = models.CharField(max_length=100) severity = models.SmallIntegerField(default=0) open_date = models.DateTimeField() close_date = models.DateTimeField() status = models.SmallIntegerField(default=0) def __str__(self): return self.title

Estoy en Django 1.10