fix(options): enable using plugin without defining options (#393)

Author: kevinchappell

package-lock.json

@@ -120,7 +120,7 @@ class CssModuleFactory {
 }
 
 class MiniCssExtractPlugin {
-  constructor(options) {
+  constructor(options = {}) {
     this.options = Object.assign(
       {
         filename: DEFAULT_FILENAME,

src/index.js

@@ -0,0 +1,2 @@
+body { background: red; }
+

test/cases/default-options/expected/main.css

@@ -0,0 +1 @@
+import './style.css';

test/cases/default-options/index.js

@@ -0,0 +1 @@
+body { background: red; }

test/cases/default-options/style.css

@@ -0,0 +1,14 @@
+import Self from '../../../src';
+
+module.exports = {
+  entry: './index.js',
+  module: {
+    rules: [
+      {
+        test: /\.css$/,
+        use: [Self.loader, 'css-loader'],
+      },
+    ],
+  },
+  plugins: [new Self()],
+};