Error when migrating from draft7 to draft2019

I ran: `ajv migrate -s schema.json --spec draft2019 -o schema2019.json`

And I get the following error:
```
ajv-cli\node_modules\ajv\dist\core.js:127
throw new Error(`no schema with key or ref "${schemaKeyRef}"`);
^
Error: no schema with key or ref "http://json-schema.org/draft-07/schema#"
at Ajv2019.validate (ajv-cli\node_modules\ajv\dist\core.js:127:23)
at Ajv2019.validateSchema (ajv-cli\node_modules\ajv\dist\core.js:238:28)
at migrateSchema (ajv-cli\dist\commands\migrate.js:37:31)
```

Let me know if it is user error, but draft4 to both draft7 and draft2019 works fine.