feat: ignore falsy values in prepends/appends/deps, so it is easier for user to do conditional config

Author: 3cp

spec/bundler.spec.js

@@ -77,7 +77,7 @@ test('Bundler traces files', t => {
     'node_modules/loo/loo.js': '',
   };
   const bundler = createBundler(fakeFs, {
-    prepends: ['var pre = 1;', 'local/setup.js'],
+    prepends: ['var pre = 1;', '', undefined, false, 'local/setup.js', null],
     appends: ['local/after.js', 'var ape = 1;']
   });
 

src/index.js

@@ -50,14 +50,14 @@ export default class Bundler {
     this._depsFinder = opts.depsFinder;
     this._onRequire = opts.onRequire || opts.onrequire || opts.onRequiringModule;
 
-    this._prepends = opts.prepends || opts.prepend || [];
+    this._prepends = (opts.prepends || opts.prepend || []).filter(t => t);
     this._prepends.push(
       // load dumber-module-loader after prepends
       path.join(_resolve('dumber-module-loader'), 'dist/index.js')
     );
-    this._appends = opts.appends || opts.append || [];
+    this._appends = (opts.appends || opts.append || []).filter(t => t);
 
-    this._dependencies = (opts.dependencies || opts.deps || []).map(d => new Package(d));
+    this._dependencies = (opts.dependencies || opts.deps || []).filter(t => t).map(d => new Package(d));
     this._entryBundle = stripJsExtension(opts.entryBundle) || 'entry-bundle';
     this._codeSplit = opts.codeSplit || function(){};
     // mark dirtiness of bundles