Define no proxy but get 'When "proxy" is specified in package.json' error - node.js

Question

When I run npm run dev I get an error message:
When "proxy" is specified in package.json it must start with either http:// or https:// , but I don't define any proxy in my package.json. How can this happen and how do I solve it?
package.json
{
"name": "vue-admin-template",
"version": "4.3.0",
"description": "A vue admin template with Element UI & axios & iconfont & permission control & lint",
"author": "Pan <panfree23#gmail.com>",
"license": "MIT",
"scripts": {
"dev": "vue-cli-service serve",
"build:prod": "vue-cli-service build",
"build:stage": "vue-cli-service build --mode staging",
"preview": "node build/index.js --preview",
"lint": "eslint --ext .js,.vue src",
"test:unit": "jest --clearCache && vue-cli-service test:unit",
"test:ci": "npm run lint && npm run test:unit",
"svgo": "svgo -f src/icons/svg --config=src/icons/svgo.yml"
},
"dependencies": {
"#gitgraph/js": "^1.3.5",
"#toast-ui/vue-editor": "^2.5.1",
"axios": "0.18.1",
"chart.js": "^2.9.4",
"chartjs-plugin-datalabels": "^0.7.0",
"echarts": "^4.8.0",
"element-ui": "2.13.2",
"element-ui-el-table-draggable": "^1.2.9",
"fuse.js": "^6.4.3",
"jquery": "^3.5.1",
"js-cookie": "2.2.0",
"jwt-simple": "^0.5.6",
"moment": "^2.27.0",
"monaco-editor": "^0.20.0",
"monaco-editor-webpack-plugin": "^1.9.0",
"normalize.css": "7.0.0",
"nprogress": "0.2.0",
"path-to-regexp": "2.4.0",
"socket.io-client": "^4.0.0",
"tui-editor": "1.3.3",
"vue": "2.6.10",
"vue-chartjs": "^3.5.1",
"vue-i18n": "^8.22.1",
"vue-jwt-decode": "^0.1.0",
"vue-router": "3.0.6",
"vue-showdown": "^2.4.1",
"vuedraggable": "2.20.0",
"vuex": "3.1.0",
"wangeditor": "^3.1.1"
},
"devDependencies": {
"#vue/cli-plugin-babel": "3.6.0",
"#vue/cli-plugin-eslint": "^3.9.1",
"#vue/cli-plugin-unit-jest": "3.6.3",
"#vue/cli-service": "3.6.0",
"#vue/test-utils": "1.0.0-beta.29",
"autoprefixer": "^9.5.1",
"babel-core": "7.0.0-bridge.0",
"babel-eslint": "10.0.1",
"babel-jest": "23.6.0",
"chalk": "2.4.2",
"connect": "3.6.6",
"eslint": "5.15.3",
"eslint-plugin-vue": "5.2.2",
"html-webpack-plugin": "3.2.0",
"mockjs": "1.0.1-beta3",
"runjs": "^4.3.2",
"sass": "^1.26.8",
"sass-loader": "^7.1.0",
"script-ext-html-webpack-plugin": "2.1.3",
"serve-static": "^1.13.2",
"svg-sprite-loader": "4.1.3",
"svgo": "1.2.2",
"vue-template-compiler": "2.6.10"
},
"engines": {
"node": ">=8.9",
"npm": ">= 3.0.0"
},
"browserslist": [
"> 1%",
"last 2 versions"
]
}

Answer 1

It was in vue.config.js. Setting wrong proxy here will occur the same error message.