title: Flask-Migrate: index has table none
body: <p>I am trying to create the migration:</p>
  
  <blockquote>
    <p>python manage.py db migrate</p>
  </blockquote>
  
  <p>Getting the following stack trace:
  I tracked it down to the </p>
  
  <pre><code>[2019-08-12 17:09:11,197] INFO in __init__: Project API
  INFO  [alembic.runtime.migration] Context impl OracleImpl.
  INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
  INFO  [alembic.autogenerate.compare] Detected removed table 'program'
  INFO  [alembic.autogenerate.compare] Detected removed index 'alerts_idx' on 'alerts'
  INFO  [alembic.autogenerate.compare] Detected removed table 'alerts'
  INFO  [alembic.autogenerate.compare] Detected removed index 'error_log_err_date_idx' on 'error_log'
  Traceback (most recent call last):
    File ".vscode\extensions\ms-python.python-2019.8.29288\pythonFiles\ptvsd_launcher.py", line 43, in &lt;module&gt;
      main(ptvsdArgs)
    File ".vscode\extensions\ms-python.python-2019.8.29288\pythonFiles\lib\python\ptvsd\__main__.py", line 432, in main
      run()
    File "Desktop\Project\MVP\myVE\lib\site-packages\alembic\autogenerate\compare.py", line 612, in obj_removed
      modify_ops.ops.append(ops.DropIndexOp.from_index(obj.const))
    File "Desktop\Project\MVP\myVE\lib\site-packages\alembic\operations\ops.py", line 1026, in from_index
      index.table.name,
  AttributeError: 'NoneType' object has no attribute 'name'
  </code></pre>
  
  <p><strong><em>Trimed for bravity</em></strong></p>