prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  order_expiry_time migration error
  **Describe the bug**
  The latest migration, `2c7ff9781032` had a bug where the server_default was supposed to be a string. 
  
  
  **Additional context**
  Working on it.
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `migrations/versions/2c7ff9781032_.py`
  Content:
  ```
  1 """empty message
  2 
  3 Revision ID: 2c7ff9781032
  4 Revises: b08a4ffff5dd
  5 Create Date: 2019-06-21 04:33:59.021835
  6 
  7 """
  8 
  9 from alembic import op
  10 import sqlalchemy as sa
  11 import sqlalchemy_utils
  12 
  13 
  14 # revision identifiers, used by Alembic.
  15 revision = '2c7ff9781032'
  16 down_revision = 'b08a4ffff5dd'
  17 
  18 
  19 def upgrade():
  20     # ### commands auto generated by Alembic - please adjust! ###
  21     op.drop_column('events', 'order_expiry_time')
  22     op.drop_column('events_version', 'order_expiry_time')
  23     op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), default=15, nullable=False))
  24     # ### end Alembic commands ###
  25 
  26 
  27 def downgrade():
  28     # ### commands auto generated by Alembic - please adjust! ###
  29     op.drop_column('settings', 'order_expiry_time')
  30     op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))
  31     op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))
  32     # ### end Alembic commands ###
  33
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/migrations/versions/2c7ff9781032_.py b/migrations/versions/2c7ff9781032_.py
  --- a/migrations/versions/2c7ff9781032_.py
  +++ b/migrations/versions/2c7ff9781032_.py
  @@ -20,13 +20,13 @@
       # ### commands auto generated by Alembic - please adjust! ###
       op.drop_column('events', 'order_expiry_time')
       op.drop_column('events_version', 'order_expiry_time')
  -    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), default=15, nullable=False))
  +    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), server_default='15', nullable=False))
       # ### end Alembic commands ###
   
   
   def downgrade():
       # ### commands auto generated by Alembic - please adjust! ###
       op.drop_column('settings', 'order_expiry_time')
  -    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))
  -    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))
  +    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))
  +    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))
       # ### end Alembic commands ###
  
verification_info: {"golden_diff": "diff --git a/migrations/versions/2c7ff9781032_.py b/migrations/versions/2c7ff9781032_.py\n--- a/migrations/versions/2c7ff9781032_.py\n+++ b/migrations/versions/2c7ff9781032_.py\n@@ -20,13 +20,13 @@\n     # ### commands auto generated by Alembic - please adjust! ###\n     op.drop_column('events', 'order_expiry_time')\n     op.drop_column('events_version', 'order_expiry_time')\n-    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), default=15, nullable=False))\n+    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), server_default='15', nullable=False))\n     # ### end Alembic commands ###\n \n \n def downgrade():\n     # ### commands auto generated by Alembic - please adjust! ###\n     op.drop_column('settings', 'order_expiry_time')\n-    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))\n-    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))\n+    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))\n+    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))\n     # ### end Alembic commands ###\n", "issue": "order_expiry_time migration error\n**Describe the bug**\r\nThe latest migration, `2c7ff9781032` had a bug where the server_default was supposed to be a string. \r\n\r\n\r\n**Additional context**\r\nWorking on it.\n", "before_files": [{"content": "\"\"\"empty message\n\nRevision ID: 2c7ff9781032\nRevises: b08a4ffff5dd\nCreate Date: 2019-06-21 04:33:59.021835\n\n\"\"\"\n\nfrom alembic import op\nimport sqlalchemy as sa\nimport sqlalchemy_utils\n\n\n# revision identifiers, used by Alembic.\nrevision = '2c7ff9781032'\ndown_revision = 'b08a4ffff5dd'\n\n\ndef upgrade():\n    # ### commands auto generated by Alembic - please adjust! ###\n    op.drop_column('events', 'order_expiry_time')\n    op.drop_column('events_version', 'order_expiry_time')\n    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), default=15, nullable=False))\n    # ### end Alembic commands ###\n\n\ndef downgrade():\n    # ### commands auto generated by Alembic - please adjust! ###\n    op.drop_column('settings', 'order_expiry_time')\n    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))\n    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=False))\n    # ### end Alembic commands ###\n", "path": "migrations/versions/2c7ff9781032_.py"}], "after_files": [{"content": "\"\"\"empty message\n\nRevision ID: 2c7ff9781032\nRevises: b08a4ffff5dd\nCreate Date: 2019-06-21 04:33:59.021835\n\n\"\"\"\n\nfrom alembic import op\nimport sqlalchemy as sa\nimport sqlalchemy_utils\n\n\n# revision identifiers, used by Alembic.\nrevision = '2c7ff9781032'\ndown_revision = 'b08a4ffff5dd'\n\n\ndef upgrade():\n    # ### commands auto generated by Alembic - please adjust! ###\n    op.drop_column('events', 'order_expiry_time')\n    op.drop_column('events_version', 'order_expiry_time')\n    op.add_column('settings', sa.Column('order_expiry_time', sa.Integer(), server_default='15', nullable=False))\n    # ### end Alembic commands ###\n\n\ndef downgrade():\n    # ### commands auto generated by Alembic - please adjust! ###\n    op.drop_column('settings', 'order_expiry_time')\n    op.add_column('events_version', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))\n    op.add_column('events', sa.Column('order_expiry_time', sa.INTEGER(), autoincrement=False, nullable=True))\n    # ### end Alembic commands ###\n", "path": "migrations/versions/2c7ff9781032_.py"}]}