exportPathMap is an async function that receives 2 arguments: the first one is defaultPathMap, which is the default map used by Next.js. The second argument is an object with:
dev - true when exportPathMap is being called in development. false when running next export. In development exportPathMap is used to define routes.
dir - Absolute path to the project directory
outDir - Absolute path to the out/ directory (configurable with -o). When dev is true the value of outDir will be null.
distDir - Absolute path to the .next/ directory (configurable with the distDir config)
buildId - The generated build id
The returned object is a map of pages where the key is the pathname and the value is an object that accepts the following fields:
page: String - the page inside the pages directory to render