title: Django `migrate` command fails with: ValueError: invalid literal for int() with base 10: '' "IntegerField"
body: <p>Can you explain it to me? Why this is my models.py? I get this error message: ValueError: invalid literal for int() with base 10: ''</p>
  
  <pre><code>from django.db import models
  
  # Create your models here.
  
  class Contact(models.Model):
      first_name = models.CharField(
          max_length=255,
      )
      last_name = models.CharField(
          max_length=255,
      )
      email = models.EmailField(
          max_length=255,
      )
      nomor_hp = models.IntegerField(
  
      )
  </code></pre>