add migration to fix preferred timezone

migrations/versions/0407_fix_preferred_timezone.py

@@ -0,0 +1,18 @@
+"""
+
+Revises: 0406_adjust_agreement_model
+
+"""
+from alembic import op
+
+down_revision = "0406_adjust_agreement_model"
+revision = "0407_fix_preferred_timezone"
+
+
+def upgrade():
+    op.execute("update users set preferred_timezone='US/Eastern' where preferred_timezone=''")
+
+
+
+def downgrade():
+    pass