apollo angular how to use a nullable but required argument in mutations?

Question

I would like to use a typescript interface for an update mutation:

export interface UpdateDescription {
  title: string;
  publishedFrom: date | null;
}

So if null is passed as value of publishedFrom, the original date should be removed on the server. If the key would be optional and publishedFrom is not provided, but in the model there already is set a value, it would be removed as well. This is not an option! Is there is possibility to write a mutation like:

mutation UpdateExample($id: ID!, $title: String!, $publishedFrom: ISO8601DateTime!) {
  updateExample(input: {id: $id, title: $title, publishedFrom: $publishedFrom}) {
    errors
  }
}

and make publishedFrom required but nullable?