Fix error resolving output path

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Error: Invalid path src/main/webapp/js/alm/builds/pages/
    at pathToArray (/Users/kharriger/projects/alm/alm-webapp/node_modules/webpack-dev-server/node_modules/webpack-dev-middleware/node_modules/memory-fs/lib/MemoryFileSystem.js:23:38)
    at MemoryFileSystem.mkdirpSync (/Users/kharriger/projects/alm/alm-webapp/node_modules/webpack-dev-server/node_modules/webpack-dev-middleware/node_modules/memory-fs/lib/MemoryFileSystem.js:107:13)
    at MemoryFileSystem.(anonymous function) [as mkdirp] (/Users/kharriger/projects/alm/alm-webapp/node_modules/webpack-dev-server/node_modules/webpack-dev-middleware/node_modules/memory-fs/lib/MemoryFileSystem.js:187:34)
    at Tapable.<anonymous> (/Users/kharriger/projects/alm/alm-webapp/node_modules/webpack/lib/Compiler.js
Could you test for the cases when `webpackOptions.output` or `webpackOptions.output.path` is not set... They are both optional...