Fix migration script and user model

migrations/versions/3f76448bb6de_add_user_confirmed_column.py

@@ -8,7 +8,6 @@ Create Date: 2019-12-21 17:11:36.564632
 from alembic import op
 import sqlalchemy as sa
 
-
 # revision identifiers, used by Alembic.
 revision = '3f76448bb6de'
 down_revision = 'b0fea72a3f20'
@@ -18,7 +17,9 @@ depends_on = None
 
 def upgrade():
     with op.batch_alter_table('user') as batch_op:
-        batch_op.add_column(sa.Column('confirmed', sa.Boolean()))
+        batch_op.add_column(
+            sa.Column('confirmed', sa.Boolean(), nullable=False,
+                      default=False))
 
 
 def downgrade():