Flask-Migrate: KeyError: 'migrate' on heroku

when I try to run heroku flask db migrate or heroku flask db upgrade on Heroku. Heroku gives me the error below:

Traceback (most recent call last): File “/app/.heroku/python/bin/flask”, line 8, in <module> sys.exit(main()) File “/app/.heroku/python/lib/python3.6/site-packages/flask/cli.py”, line 967, in main cli.main(args=sys.argv[1:], prog_name=“python -m flask” if as_module else None) File “/app/.heroku/python/lib/python3.6/site-packages/flask/cli.py”, line 586, in main return super(FlaskGroup, self).main(*args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 782, in main rv = self.invoke(ctx) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 1259, in invoke return _process_result(sub_ctx.command.invoke(sub_ctx)) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 1259, in invoke return _process_result(sub_ctx.command.invoke(sub_ctx)) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 1066, in invoke return ctx.invoke(self.callback, **ctx.params) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 610, in invoke return callback(*args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/click/decorators.py”, line 21, in new_func return f(get_current_context(), *args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/flask/cli.py”, line 426, in decorator return __ctx.invoke(f, *args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/click/core.py”, line 610, in invoke return callback(*args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/flask_migrate/cli.py”, line 134, in upgrade _upgrade(directory, revision, sql, tag, x_arg) File “/app/.heroku/python/lib/python3.6/site-packages/flask_migrate/init.py”, line 96, in wrapped f(*args, **kwargs) File “/app/.heroku/python/lib/python3.6/site-packages/flask_migrate/init.py”, line 269, in upgrade config = current_app.extensions[‘migrate’].migrate.get_config(directory, KeyError: ‘migrate’