Schema validation failed with the following errors: Data path \".builders[\'app-shell\']\" should have required property \'class\'. Schema validation failed with the
Try to update the package.json file so that "@angular-devkit/build-angular": "^0.800.1" reads "@angular-devkit/build-angular": "^0.12.4"
package.json
"@angular-devkit/build-angular": "^0.800.1"
"@angular-devkit/build-angular": "^0.12.4"
Then run npm install in the command line.
npm install
Reference: https://stackoverflow.com/a/56537342