Error
Traceback (most recent call last):
  File "/home/radoslaw/PycharmProjects/django_school/tests/lessons/test_forms.py", line 42, in test_valid
    self.assertTrue(formset.is_valid())
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/formsets.py", line 321, in is_valid
    self.errors
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/formsets.py", line 304, in errors
    self.full_clean()
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/formsets.py", line 361, in full_clean
    form_errors = form.errors
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/forms.py", line 170, in errors
    self.full_clean()
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/forms.py", line 374, in full_clean
    self._post_clean()
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/forms/models.py", line 413, in _post_clean
    self.instance.full_clean(exclude=exclude, validate_unique=False)
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/db/models/base.py", line 1223, in full_clean
    self.clean()
  File "/home/radoslaw/PycharmProjects/django_school/django_school/apps/lessons/models.py", line 112, in clean
    if self.student.school_class != self.lesson_session.lesson.school_class:
  File "/home/radoslaw/.local/share/virtualenvs/django_school-b1r-K0kH/lib/python3.8/site-packages/django/db/models/fields/related_descriptors.py", line 197, in __get__
    raise self.RelatedObjectDoesNotExist(
django_school.apps.lessons.models.Presence.student.RelatedObjectDoesNotExist: Presence has no student.