title: Error with Django fields ["'' value has an invalid format. It must be in YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ] format."]
body: <p>Can everyone be helpful in this situation:
  I have a project in pythonanywhere host.
  I created models and register in admin.But after make migrations command I write migrate and have this error:
   File "/usr/lib/python3.7/site-packages/django/db/models/fields/<strong>init</strong>.py", line 1399, in to_python
      params={'value': value},
  django.core.exceptions.ValidationError: ["'' value has an invalid format. It must be in YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ] format."]</p>
  
  <p>There is my code:</p>
  
  <p>models.py</p>
  
  <pre><code>from django.db import models
  
  
  class User(models.Model):
      login = models.CharField(max_length=50)
      passw = models.CharField(max_length=50)
      email = models.CharField(max_length=50)
      regdate = models.DateTimeField()
      status = models.CharField(max_length=50)
  
  
  
  class Category(models.Model):
      name = models.CharField(max_length=200, db_index=True)
      slug = models.SlugField(max_length=200, db_index=True, unique=True)
  
      class Meta:
          ordering = ('name',)
          verbose_name = 'Категория'
          verbose_name_plural = 'Категории'
  
      def __str__(self):
          return self.name
  
  
  class Product(models.Model):
      category = models.ForeignKey(Category, related_name='products', on_delete=models.CASCADE)
      name = models.CharField(max_length=200, db_index=True)
      slug = models.SlugField(max_length=200, db_index=True)
      description = models.TextField(blank=True)
      price = models.DecimalField(max_digits=10, decimal_places=2)
      available = models.BooleanField(default=True)
      created = models.DateTimeField(auto_now_add=True)
      updated = models.DateTimeField(auto_now=True)
  
  
      class Meta:
          ordering = ('name',)
          index_together = (('id', 'slug'),)
  
      def __str__(self):
          return self.name
  </code></pre>
  
  <p>admin.py</p>
  
  <pre><code>from django.contrib import admin
  from .models import Category, Product
  
  @admin.register(Category)
  class CategoryAdmin(admin.ModelAdmin):
      list_display = ['name', 'slug']
      prepopulated_fields = {'slug': ('name',)}
  
  
  @admin.register(Product)
  class ProductAdmin(admin.ModelAdmin):
      list_display = ['name', 'slug', 'price', 'available', 'created', 'updated']
      list_filter = ['available', 'created', 'updated']
      list_editable = ['price', 'available']
      prepopulated_fields = {'slug': ('name',)}
  </code></pre>
  
  <p>please, somebody explain me my mistake.I stuck with this.....Thanks a lot!!!!!!!</p>