new_contents: # Generated by Django 2.2.12 on 2020-05-25 07:00
  
  from django.db import migrations, models
  import projects.source_models
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('projects', '0042_elifesource'),
      ]
  
      operations = [
          migrations.AlterField(
              model_name='source',
              name='project',
              field=models.ForeignKey(blank=True, null=True, on_delete=projects.source_models.NON_POLYMORPHIC_CASCADE, related_name='sources', to='projects.Project'),
          ),
      ]
  
subject: Add migration