An unhandled exception occurred: Could not find the implementation for builder @angular-devkit/build-angular:dev-server-Twitter bootstrap

I was trying to install ngb-tabset, and I got some error on angular-core, which accordingly I ran:

npm install -S @angular/material @angular/cdk @angular/animations

npm uninstall @angular/core

npm install -S @angular/core

But then I got some other error… for which I did npm update, then again few errors. I did:

rm -rf node_modules
npm install

Then I started getting the below error.

An unhandled exception occurred: Could not find the implementation for
builder @angular-devkit/build-angular:dev-server
See “/tmp/ng-2tgkqg/angular-errors.log” for further details.

I tried to do –

npm install --save-dev @angular-devkit/build-angular

but of no use.

And my package.json is –

{
  "name": "@coreui/coreui-free-angular-admin-template",
  "version": "2.0.1",
  "description": "CoreUI Free Angular 2+ Admin Template",
  "author": {
    "name": "Łukasz Holeczek",
    "url": "http://holeczek.pl",
    "github": "https://github.com/mrholek",
    "twitter": "https://twitter.com/lukaszholeczek"
  },
  "contributors": [
    {
      "name": "Andrzej Kopański",
      "url": "https://github.com/xidedix"
    }
  ],
  "homepage": "https://coreui.io/angular",
  "copyright": "Copyright 2018 creativeLabs Łukasz Holeczek",
  "license": "MIT",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build --prod",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@agm/core": "^1.0.0-beta.5",
    "@angular/animations": "^6.1.10",
    "@angular/cdk": "^7.3.3",
    "@angular/common": "^6.1.10",
    "@angular/compiler": "^6.1.10",
    "@angular/core": "^6.1.10",
    "@angular/forms": "^6.1.10",
    "@angular/http": "^6.1.10",
    "@angular/material": "^7.3.3",
    "@angular/platform-browser": "^6.1.10",
    "@angular/platform-browser-dynamic": "^6.1.10",
    "@angular/router": "^6.1.10",
    "@coreui/angular": "^2.0.0-rc.1",
    "@coreui/coreui": "^2.0.20",
    "@coreui/coreui-plugin-chartjs-custom-tooltips": "^1.2.0",
    "@coreui/icons": "^0.3.0",
    "@ng-select/ng-select": "^2.16.0",
    "@progress/kendo-angular-buttons": "^4.0.0",
    "@progress/kendo-angular-dateinputs": "2 - 3",
    "@progress/kendo-angular-dropdowns": "2 - 3",
    "@progress/kendo-angular-excel-export": "1 - 2",
    "@progress/kendo-angular-grid": "^3.13.0",
    "@progress/kendo-angular-inputs": "2 - 4",
    "@progress/kendo-angular-intl": "^1.0.0",
    "@progress/kendo-angular-l10n": "^1.1.0",
    "@progress/kendo-angular-popup": "^2.0.0",
    "@progress/kendo-data-query": "^1.0.0",
    "@progress/kendo-drawing": "^1.0.0",
    "@progress/kendo-theme-default": "latest",
    "@syncfusion/ej2-angular-dropdowns": "^16.4.55",
    "@syncfusion/ej2-angular-grids": "^16.4.55",
    "@syncfusion/ej2-ng-dropdowns": "^16.2.50",
    "@types/jquery": "^3.3.29",
    "angular-confirmation-popover": "^4.2.0",
    "angular-neo4j": "^0.7.1",
    "angular2-bootstrap-switch": "^0.2.3",
    "angular2-countrypicker": "^1.0.0",
    "angular2-google-maps": "^0.17.0",
    "apriori": "^1.0.7",
    "bcryptjs": "^2.4.3",
    "bootstrap": "^4.0.0-beta.3",
    "chart.js": "^2.7.3",
    "core-js": "^2.6.5",
    "cors": "^2.8.5",
    "country-select-js": "^2.0.1",
    "crud-sdk": "0.0.30",
    "cryptr": "^4.0.2",
    "csv-writer": "^1.2.0",
    "express": "^4.16.4",
    "express-jwt": "^5.3.1",
    "express-session": "^1.15.6",
    "file-saver": "^2.0.1",
    "flag-icon-css": "^3.2.1",
    "font-awesome": "^4.7.0",
    "html2canvas": "^1.0.0-rc.3",
    "html2pdf.js": "^0.9.1",
    "jquery": "^3.4.0",
    "jspdf": "^1.5.3",
    "jspdf-autotable": "^3.1.1",
    "login-sdk": "0.0.3",
    "mkdirp": "^0.5.1",
    "moment": "^2.22.2",
    "mongodb": "^2.2.33",
    "mongoskin": "^2.0.3",
    "morgan": "^1.9.1",
    "multer": "^1.4.1",
    "mutationobserver-shim": "^0.3.2",
    "nemex-angular2-realtimegeolocation": "0.0.6",
    "ng-multiselect-dropdown": "^0.2.3",
    "ng2-charts": "^1.6.0",
    "ng2-opd-popup": "^1.1.21",
    "ng2-select": "^2.0.0",
    "ngx-accordion": "0.0.17",
    "ngx-bootstrap": "^3.3.0",
    "ngx-country-select": "^2.0.6",
    "ngx-horizontal-timeline": "0.0.5",
    "ngx-loading": "^3.0.1",
    "ngx-mat-select-search": "^1.5.3",
    "ngx-pagination": "^3.2.1",
    "ngx-perfect-scrollbar": "^6.3.1",
    "ngx-scrollbar": "^3.2.2",
    "ngx-select-dropdown": "^1.0.1",
    "ngx-smart-modal": "^7.1.1",
    "ngx-ui-switch": "^8.0.0",
    "nodemailer": "^5.0.0",
    "nodemon": "^1.19.1",
    "notification-sdk": "0.0.9",
    "pdfmake": "^0.1.57",
    "primeicons": "^1.0.0",
    "primeng": "^7.1.3",
    "q": "^1.5.1",
    "redis": "^2.8.0",
    "request": "^2.88.0",
    "request-promise": "^4.2.2",
    "request-promise-native": "^1.0.5",
    "restify": "^7.2.2",
    "rootpath": "^0.1.2",
    "rxjs": "^6.4.0",
    "rxjs-compat": "^6.0.0",
    "simple-line-icons": "^2.4.1",
    "tinyurl": "^1.1.2",
    "ts-helpers": "^1.1.2",
    "tsickle": "^0.33.0",
    "tslib": "^1.10.0",
    "venn.js": "^0.2.20",
    "web-animations-js": "^2.3.1",
    "zone.js": "^0.8.29"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "^0.7.5",
    "@angular/cli": "^6.2.7",
    "@angular/compiler-cli": "^6.1.10",
    "@angular/language-service": "^6.1.10",
    "@types/jasmine": "^2.8.9",
    "@types/jasminewd2": "^2.0.5",
    "@types/node": "^10.14.4",
    "body-parser": "^1.18.3",
    "codelyzer": "^4.5.0",
    "jasmine-core": "^3.2.1",
    "jasmine-spec-reporter": "^4.2.1",
    "karma": "^3.0.0",
    "karma-chrome-launcher": "^2.2.0",
    "karma-coverage-istanbul-reporter": "^2.0.4",
    "karma-jasmine": "^1.1.2",
    "karma-jasmine-html-reporter": "^1.3.1",
    "protractor": "^5.4.1",
    "ts-node": "^7.0.1",
    "tslint": "^5.11.0",
    "typescript": "^2.9.2"
  },
  "engines": {
    "node": ">= 8.9.4",
    "npm": ">= 5.6.0"
  }
}

angular.json

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "newProjectRoot": "projects",
  "projects": {
    "ng": {
      "root": "",
      "sourceRoot": "src",
      "projectType": "application",
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "outputPath": "dist",
            "index": "src/index.html",
            "main": "src/main.ts",
            "tsConfig": "src/tsconfig.app.json",
            "polyfills": "src/polyfills.ts",
            "assets": [
              "src/assets"
            ],
            "styles": [
              "./node_modules/bootstrap/dist/css/bootstrap.css",
              "node_modules/bootstrap/dist/css/bootstrap.min.css",
              "./node_modules/ngx-bootstrap/datepicker/bs-datepicker.css",
              "node_modules/@coreui/icons/css/coreui-icons.css",
              "node_modules/flag-icon-css/css/flag-icon.css",
              "node_modules/font-awesome/css/font-awesome.css",
              "node_modules/simple-line-icons/css/simple-line-icons.css",
              "src/scss/style.scss",
              "./node_modules/ngx-ui-switch/ui-switch.component.css",
              "node_modules/ngx-smart-modal/ngx-smart-modal.scss"
            ],
            "stylePreprocessorOptions": {
              "includePaths": [
                "./node_modules"
              ]
            },
            "scripts": [
              "node_modules/chart.js/dist/Chart.min.js"
            ]
          },
          "configurations": {
            "production": {
              "optimization": true,
              "outputHashing": "all",
              "sourceMap": false,
              "extractCss": true,
              "namedChunks": false,
              "aot": true,
              "extractLicenses": true,
              "vendorChunk": false,
              "buildOptimizer": true,
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.ts",
                  "with": "src/environments/environment.prod.ts"
                }
              ]
            }
          }
        },
        "serve": {
          "builder": "@angular-devkit/build-angular:dev-server",
          "options": {
            "browserTarget": "ng:build"
          },
          "configurations": {
            "production": {
              "browserTarget": "ng:build:production"
            }
          }
        },
        "extract-i18n": {
          "builder": "@angular-devkit/build-angular:extract-i18n",
          "options": {
            "browserTarget": "ng:build"
          }
        },
        "test": {
          "builder": "@angular-devkit/build-angular:karma",
          "options": {
            "main": "src/test.ts",
            "karmaConfig": "./karma.conf.js",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "src/tsconfig.spec.json",
            "scripts": [
              "node_modules/chart.js/dist/Chart.min.js"
            ],
            "styles": [
              "node_modules/bootstrap/dist/css/bootstrap.css",
              "./node_modules/ngx-bootstrap/datepicker/bs-datepicker.css",
              {
                "input": "node_modules/@progress/kendo-theme-default/dist/all.css"
              },
              "node_modules/flag-icon-css/css/flag-icon.css",
              "node_modules/font-awesome/css/font-awesome.css",
              "node_modules/simple-line-icons/css/simple-line-icons.css",
              "src/scss/style.scss"
            ],
            "stylePreprocessorOptions": {
              "includePaths": [
                "./node_modules"
              ]
            },
            "assets": [
              "src/assets",
              "src/favicon.ico"
            ]
          }
        },
        "lint": {
          "builder": "@angular-devkit/build-angular:tslint",
          "options": {
            "tsConfig": [
              "src/tsconfig.app.json",
              "src/tsconfig.spec.json"
            ],
            "exclude": [
              "**/node_modules/**"
            ]
          }
        }
      }
    },
    "ng-e2e": {
      "root": "",
      "sourceRoot": "",
      "projectType": "application",
      "architect": {
        "e2e": {
          "builder": "@angular-devkit/build-angular:protractor",
          "options": {
            "protractorConfig": "./protractor.conf.js",
            "devServerTarget": "ng:serve"
          }
        },
        "lint": {
          "builder": "@angular-devkit/build-angular:tslint",
          "options": {
            "tsConfig": [
              "e2e/tsconfig.e2e.json"
            ],
            "exclude": [
              "**/node_modules/**"
            ]
          }
        }
      }
    }
  },
  "defaultProject": "ng",
  "schematics": {
    "@schematics/angular:component": {
      "prefix": "app",
      "styleext": "scss"
    },
    "@schematics/angular:directive": {
      "prefix": "app"
    }
  }
}