Populate.keyField ignored?

We are trying to use the keyField parameter to use _id instead of id

_id: { type: "string", primaryKey: true },

country: {
        type: "string",
        required: true,
        populate: {
          keyField: "_id",
          action: "countries.get",
        },
      },

But we are getting validation errors on countries.get saying that _id is undefined. Seems like id is hardcoded?
https://github.com/moleculerjs/database/blob/3e962ec89f191d8c3a4de25eb8e7cfb2390e9716/src/transform.js#L186-L190

Here's a workaround we found:

country: {
        type: "string",
        required: true,
        populate: async (ctx, values, entities, field) => {
          return Promise.all(
            entities.map(
              async (entity) =>
                (entity.postCount = await ctx.call(
                  "countries.get",
                  { _id: entity.country }
                ))
            )
          );
        },
      },

Start in src/transform.js around lines 186-190 and trace how populate.keyField is used when building the countries.get call. Reproduce the schema with _id as the primary key; done means keyField: "_id" is honored without the validation error described in the issue.