The root value has an unexpected property

[alvarlagerlof]

- The root value has an unexpected property, 0, which is not in the list of allowed properties (amp, analyticsId, assetPrefix, basePath, cleanDistDir, compiler, compress, crossOrigin, devIndicators, distDir, env, eslint, excludeDefaultMomentLocales, experimental, exportPathMap, future, generateBuildId, generateEtags, headers, httpAgentOptions, i18n, images, onDemandEntries, optimizeFonts, output, outputFileTracing, pageExtensions, poweredByHeader, productionBrowserSourceMaps, publicRuntimeConfig, reactStrictMode, redirects, rewrites, sassOpt

I get this when I build.