title: AssertionError: First parameter to ForeignKey must be either a model, a model name, or the string 'self'
body: <p>I just created a model like this :</p>
  <pre><code>from django.db import models
  
  # Create your models here.
  
  
  class Category:
      title = models.CharField(max_length=50)
      slug = models.CharField(max_length=200)
      cat_image = models.ImageField(upload_to='images/')
  
      def __str__(self):
          return self.title
  
  class Brand:
      title = models.CharField(max_length=50)
      slug = models.CharField(max_length=200)
      brand_image = models.ImageField(upload_to='images/')
  
      def __str__(self):
          return self.title
  
  class UOM:
      title = models.CharField(max_length=100)
  
      def __str__(self):
          return self.title
      
  class Product_Images:
      multi_images = models.ImageField(upload_to='images/')
  
  
  
  class Product:
      name = models.CharField(max_length=100)
      slug = models.CharField(max_length=200)
      category = models.ForeignKey(Category, on_delete=models.CASCADE)
      brand = models.ForeignKey(Brand, on_delete=models.CASCADE)
      price = models.IntegerField(null=True, blank=True)
      height = models.IntegerField(null=True, blank=True)
      weight = models.IntegerField(null=True, blank=True)
      length = models.IntegerField(null=True, blank=True)
      color = models.IntegerField(null=True, blank=True)
      stock = models.BooleanField()
      SKU = models.CharField(max_length=150)
  
  
      def __str__(self):
          return self.name
  
  
  class Customer:
      phone_number = models.CharField(max_length=11)
      first_name = models.CharField(max_length=10)
      last_name = models.CharField(max_length=10)
      email = models.CharField(max_length=20)
      password = models.CharField(max_length=10)
  
  
      def __str__(self):
          return self.first_name
  
  
  
  class Order:
      customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
      invoice = models.CharField(max_length=16, null=True, blank=True)
      phone = models.CharField(max_length=12)
      address = models.CharField(max_length=150)
      
  </code></pre>
  <p>But facing this error dont have any idea why i am getting this kind of error. I cant even makemigrations if i delete some fields. It says no change detected but i changed some fields still getting this kind of error can some one solve this issue for me. and please explain why ia magetting this kind of error i cant find any problem here. I am also facing this no changes issue on my macos also. i am changing some fields still it says no changes detected .</p>