626fad2e71
BREAKING CHANGE: To delete a field via the GraphQL API, the field value has to be set to `null`. Previously, setting a field value to `null` would save a null value in the database, which was not according to the [GraphQL specs](https://spec.graphql.org/June2018/#sec-Null-Value). To delete a file field use `file: null`, the previous way of using `file: { file: null }` has become obsolete.