add migration to fix null characters in document contents

src/documents/tests/test_migration_remove_null_characters.py

@@ -0,0 +1,15 @@
+from documents.tests.utils import DirectoriesMixin, TestMigrations
+
+
+class TestMigrateNullCharacters(DirectoriesMixin, TestMigrations):
+
+    migrate_from = '1014_auto_20210228_1614'
+    migrate_to = '1015_remove_null_characters'
+
+    def setUpBeforeMigration(self, apps):
+        Document = apps.get_model("documents", "Document")
+        self.doc = Document.objects.create(content="aaa\0bbb")
+
+    def testMimeTypesMigrated(self):
+        Document = self.apps.get_model('documents', 'Document')
+        self.assertNotIn("\0", Document.objects.get(id=self.doc.id).content)