project is a
npm run dev generated using vue-cli that can be accessed normally.
npm run build reported an error. The error message is as follows

building for production.Error processing file:
static/css/app.104df4065122c4f2c7a136e88a4e9c00.css (node:2780)
UnhandledPromiseRejectionWarning: SyntaxError: Unexpected token in
JSON at position 111054

at JSON.parse (<anonymous>)
at new SourceMapConsumer (F:\work\ror\test\buefy-sample\node_modules\_source-map@0.5.7@source-map\lib\source-map-consumer.js:17:22)
at PreviousMap.consumer (F:\work\ror\test\buefy-sample\node_modules\_postcss@5.2.18@postcss\lib\previous-map.js:69:34)
at new Input (F:\work\ror\test\buefy-sample\node_modules\_postcss@5.2.18@postcss\lib\input.js:84:28)
at parse (F:\work\ror\test\buefy-sample\node_modules\_postcss@5.2.18@postcss\lib\parse.js:21:17)
at new LazyResult (F:\work\ror\test\buefy-sample\node_modules\_postcss@5.2.18@postcss\lib\lazy-result.js:70:24)
at Processor.process (F:\work\ror\test\buefy-sample\node_modules\_postcss@5.2.18@postcss\lib\processor.js:117:12)
at Function.cssnano.process (F:\work\ror\test\buefy-sample\node_modules\_cssnano@3.10.0@cssnano\dist\index.js:306:55)
at OptimizeCssAssetsPlugin.processCss (F:\work\ror\test\buefy-sample\node_modules\_optimize-css-assets-webpack-plugin@3.2.0@optimize-css-assets-webpack-plugin\index.js:63:19)
at Object.processor (F:\work\ror\test\buefy-sample\node_modules\_optimize-css-assets-webpack-plugin@3.2.0@optimize-css-assets-webpack-plugin\index.js:29:23)
at F:\work\ror\test\buefy-sample\node_modules\_last-call-webpack-plugin@2.1.2@last-call-webpack-plugin\index.js:139:8
at arrayEach (F:\work\ror\test\buefy-sample\node_modules\_lodash@4.17.5@lodash\_arrayEach.js:15:9)
at forEach (F:\work\ror\test\buefy-sample\node_modules\_lodash@4.17.5@lodash\forEach.js:38:10)
at LastCallWebpackPlugin.process (F:\work\ror\test\buefy-sample\node_modules\_last-call-webpack-plugin@2.1.2@last-call-webpack-plugin\index.js:136:3)
at Compilation.<anonymous> (F:\work\ror\test\buefy-sample\node_modules\_last-call-webpack-plugin@2.1.2@last-call-webpack-plugin\index.js:194:12)
at next (F:\work\ror\test\buefy-sample\node_modules\_tapable@0.2.8@tapable\lib\Tapable.js:204:14)

(node:2780) UnhandledPromiseRejectionWarning: Unhandled promise
rejection. This error originated either by throwing inside of an async
function without a catch block, or by rejecting a promise which was
not handled with .catch (). (rejection id: 2) (node:2780) [DEP0018]
DeprecationWarning: Unhandled promise rejections are deprecated. In
the future, promise rejections that are not handled will terminate the
Node.js process with a non-zero exit code.

webpack.base.conf.js is as follows

"use strict"
const path = require("path")
const utils = require("./utils")
const config = require("../config")
const vueLoaderConfig = require("./vue-loader.conf")
require("babel-polyfill")
function resolve (dir) {
  return path.join(__dirname, "..", dir)
}



module.exports = {
  context: path.resolve(__dirname, "../"),
  entry: {
    app: ["babel-polyfill", "./src/main.js"],
  },
  output: {
    path: config.build.assetsRoot,
    filename: "[name].js",
    publicPath: process.env.NODE_ENV === "production"
      ? config.build.assetsPublicPath
      : config.dev.assetsPublicPath
  },
  resolve: {
    extensions: [".js", ".vue", ".json"],
    alias: {
      "vue$": "vue/dist/vue.esm.js",
      "@": resolve("src"),
    }
  },
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: "vue-loader",
        options: vueLoaderConfig
      },
      {
        test: /\.js$/,
        loader: "babel-loader",
        include: [resolve("src"), resolve("test"), resolve("node_modules/webpack-dev-server/client")]
      },
      {
        test: /\.(png|jpe?g|gif|svg)(\?.*)?$/,
        loader: "url-loader",
        options: {
          limit: 10000,
          name: utils.assetsPath("img/[name].[hash:7].[ext]")
        }
      },
      {
        test: /\.(mp4|webm|ogg|mp3|wav|flac|aac)(\?.*)?$/,
        loader: "url-loader",
        options: {
          limit: 10000,
          name: utils.assetsPath("media/[name].[hash:7].[ext]")
        }
      },
      {
        test: /\.(woff2?|eot|ttf|otf)(\?.*)?$/,
        loader: "url-loader",
        options: {
          limit: 10000,
          name: utils.assetsPath("fonts/[name].[hash:7].[ext]")
        }
      }
    ]
  },
  node: {
    // prevent webpack from injecting useless setImmediate polyfill because Vue
    // source contains it (although only uses it if it"s native).
    setImmediate: false,
    // prevent webpack from injecting mocks to Node native modules
    // that does not make sense for the client
    dgram: "empty",
    fs: "empty",
    net: "empty",
    tls: "empty",
    child_process: "empty"
  }
}

package.json

{
  "name": "buefy-sample",
  "version": "1.0.0",
  "description": "A Vue.js project",
  "author": "*****",
  "private": true,
  "scripts": {
    "dev": "webpack-dev-server --inline --progress --config build/webpack.dev.conf.js",
    "start": "npm run dev",
    "build": "node build/build.js"
  },
  "dependencies": {
    "axios": "^0.18.0",
    "babel-polyfill": "^6.26.0",
    "buefy": "^0.6.5",
    "bulma": "^0.7.1",
    "mdi": "^2.2.43",
    "vue": "^2.5.2",
    "vue-i18n": "^7.6.0",
    "vue-router": "^3.0.1"
  },
  "devDependencies": {
    "autoprefixer": "^7.1.2",
    "babel-core": "^6.22.1",
    "babel-helper-vue-jsx-merge-props": "^2.0.3",
    "babel-loader": "^7.1.1",
    "babel-plugin-syntax-jsx": "^6.18.0",
    "babel-plugin-transform-runtime": "^6.22.0",
    "babel-plugin-transform-vue-jsx": "^3.5.0",
    "babel-preset-env": "^1.3.2",
    "babel-preset-stage-2": "^6.22.0",
    "chalk": "^2.0.1",
    "copy-webpack-plugin": "^4.0.1",
    "css-loader": "^0.28.0",
    "extract-text-webpack-plugin": "^3.0.0",
    "file-loader": "^1.1.4",
    "friendly-errors-webpack-plugin": "^1.6.1",
    "html-webpack-plugin": "^2.30.1",
    "node-notifier": "^5.1.2",
    "optimize-css-assets-webpack-plugin": "^3.2.0",
    "ora": "^1.2.0",
    "portfinder": "^1.0.13",
    "postcss-import": "^11.0.0",
    "postcss-loader": "^2.0.8",
    "postcss-url": "^7.2.1",
    "rimraf": "^2.6.0",
    "semver": "^5.3.0",
    "shelljs": "^0.7.6",
    "uglifyjs-webpack-plugin": "^1.1.1",
    "url-loader": "^0.5.8",
    "vue-loader": "^13.3.0",
    "vue-style-loader": "^3.0.1",
    "vue-template-compiler": "^2.5.2",
    "webpack": "^3.6.0",
    "webpack-bundle-analyzer": "^2.9.0",
    "webpack-dev-server": "^2.9.1",
    "webpack-merge": "^4.1.0"
  },
  "engines": {
    "node": ">= 6.0.0",
    "npm": ">= 3.0.0"
  },
  "browserslist": [
    "> 1%",
    "last 2 versions",
    "not ie <= 8"
  ]
}

main.js

import Vue from "vue";
import VueRouter from "vue-router";
import App from "./App";
import Buefy from "buefy";
import "buefy/lib/buefy.css";
import "bulma/css/bulma.css";
import routes from "./config/routers.js";
import "./assets/css/style.css";
import "mdi/css/materialdesignicons.css";
import VueI18n from "vue-i18n";



Vue.use(VueI18n);
Vue.use(VueRouter);
Vue.use(Buefy);

Vue.config.productionTip = false;