title: Django how to make form fields optional
body: <p>In django how to make form field optional ? </p>
  
  <p>my model,</p>
  
  <pre><code>class Student(models.Model):
      first_name = models.CharField(max_length=30)
      last_name = models.CharField(max_length=40)
      email = models.EmailField()
  </code></pre>