next.config.js

const { PHASE_PRODUCTION_SERVER } = process.env.NODE_ENV === 'development' ? {} : require('next-server/constants');

module.exports = (phase, { defaultConfig }) => {
  if (phase === PHASE_PRODUCTION_SERVER) {
    
    return {
      /* production only config */
    }
  }
  const withCSS = require('@zeit/next-sass')
  return withCSS({})
}