Pagination: Next/Previous related to author
You are trying to merge an object of type ElementQuery with an array so your object will be transformed as an array and merged with the new array. Of course you'll end up having an array instead of a query so you can't execute it in order to fetch the entries.

Instead of merging it, why not setting the parameter directly?

{% do param.authorId(author) %}


Furthermore authors are not related to entries  (except you set them in an additional field)