What does it do?

It allow to select the "documentId" in the strapi 5 document api inside selected "fields" without tricking the TypeScript to allow so.

Why is it needed?

The requests for documentId work and return the documentId, but the typescript check does not allow it, so need to trick TypeScript with unclean as any.

How to test it?

Have objects with references and only want to get the documentId of referenced object.
Do something like the following and verify TypeScript did not complain invalid documentId field.

const entry = await strapi.documents(contentType).findOne({
  documentId: entryId,
  fields: ['documentId'],
  populate: {
    operation: { fields: ['documentId', 'phase'], populate: { organization: { fields: ['documentId'] } } },
  },
});

Without the fix tricking TypeScript with contentType as any is required, but than loosing the IntelliSense help for possible fields and other checks / info.