404.html folder causes EISDIR illegal operations, stops onPostBuild

[roxberry]

On build:

ERROR #11321  PLUGIN

"gatsby-plugin-doctype" threw an error while running the onPostBuild lifecycle:

EISDIR: illegal operation on a directory, read

Error: EISDIR: illegal operation on a directory, read

Added code to the plugin, found the cause is the 404.html folder:

public/page-data/404.html

Local hacked it:

const glob = require(`tiny-glob`)
const fs = require(`fs-extra`)

async function getContent(filePath, encoding = 'utf-8') {
  if (!filePath) {
    throw new Error('filePath required or not found')
  }

  if (fs.lstatSync(filePath).isDirectory() ) {
    console.log ('*******************' + filePath + ' is a directory')
    return null
  }
  return fs.readFile(filePath, { encoding })
}

exports.onPostBuild = async (_, { doctype = `html` }) => {
  const files = await glob(`public/**/*.html`)

  for (const file of files) {
    const originalContent = await getContent(file)

    if (originalContent == null)
    {
      continue;
    }

    const stripped = originalContent.slice(15)
    const start = `<!DOCTYPE ${doctype}>`
    const modifiedContent = `${start}${stripped}`

    await fs.writeFile(file, modifiedContent)
  }
}