"Cannot read property 'match' of undefined" on ng build --prod after updating to 6.0.0-rc.0 #10141

Angular CLI: 6.0.0-rc.0
Node: 8.11.0
OS: win32 x64
Angular: 6.0.0-rc.1
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router

@angular/cli: 6.0.0-rc.0
@angular-devkit/architect: 0.0.10
@angular-devkit/build-angular: 0.0.10
@angular-devkit/build-optimizer: 0.4.9
@angular-devkit/core: 0.4.9
@angular-devkit/schematics: 0.5.0
@ngtools/json-schema: 1.1.0
@ngtools/webpack: 6.0.0-beta.9
@schematics/angular: 0.5.0
@schematics/update: 0.5.0
typescript: 2.7.2
webpack: 4.1.0

$ ng build --prod
Cannot read property 'match' of undefined
TypeError: Cannot read property 'match' of undefined
    at Object.normalize (D:\sandbox\1.7-project\node_modules\@angular-devkit\build-angular\node_modules\@angular-devkit\core\src\virtual-fs\path.js:178:14)
    at options.fileReplacements.forEach (D:\sandbox\1.7-project\node_modules\@angular-devkit\build-angular\src\browser\index.js:99:55)
    at Array.forEach (<anonymous>)
    at BrowserBuilder.buildWebpackConfig (D:\sandbox\1.7-project\node_modules\@angular-devkit\build-angular\src\browser\index.js:98:34)
    at Observable.rxjs_1.Observable.obs [as _subscribe] (D:\sandbox\1.7-project\node_modules\@angular-devkit\build-angular\src\browser\index.js:31:38)
    at Observable.subscribe (D:\sandbox\1.7-project\node_modules\@angular-devkit\build-angular\node_modules\rxjs\internal\Observable.js:162:69)

              "fileReplacements": [
                {
                  "from": "src/environments/environment.ts",
                  "to": "dist/undefined"
                }
              ]

              "fileReplacements": [
                {
                  "src": "src/environments/environment.ts",
                  "replaceWith": "src/environments/environment.prod.ts"
                }
              ],