Can make migration in django

i cant migrate this model in django

class ApprovedCourse(models.Model):
    course_name = models.CharField(max_length=50)
    provider_college = models.ManyToManyField('processes.College', related_name="provider_college")
    prerequisites = models.ManyToManyField('ApprovedCourse', related_name="courses_that_need_this_course",null=True)
    both_needs = models.ManyToManyField('ApprovedCourse', related_name="courses_required_for_this_course",null=True)
    number_of_course_units = models.IntegerField()
    course_type = models.CharField(max_length=50)


class SemesterCourse(models.Model):
    approved_course=models.ForeignKey('ApprovedCourse', on_delete=models.CASCADE , null=True, related_name='approved_course')
    class_day_and_time = models.CharField(max_length=50)
    exam_date_and_time = jmodels.jDateTimeField()
    exam_location = models.CharField(max_length=50)
    course_professor = models.ForeignKey('users.Professor', on_delete=models.SET_NULL, null=True, related_name="professor_course")
    course_capacity = models.IntegerField()
    current_semester = models.ForeignKey('processes.Semester', on_delete=models.SET_NULL,  null=True, related_name="semester_course")

when i want to add approved_course filed and makemigration it said this message Please select a fix:

1. Provide a one-off default now (will be set on all existing rows with a null value for this column)
2. Quit and manually define a default value in models.py. Select an option:

how can i solve it?

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