bug: accept use with addPlugin only

lib/config/validator.js

@@ -43,8 +43,9 @@ class Validator {
         if (this.webpackConfig.entries.size === 0
             && this.webpackConfig.styleEntries.size === 0
             && this.webpackConfig.copyFilesConfigs.length === 0
+            && this.webpackConfig.plugins.length === 0
         ) {
-            throw new Error('No entries found! You must call addEntry() or addEntries() or addStyleEntry() or copyFiles() at least once - otherwise... there is nothing to webpack!');
+            throw new Error('No entries found! You must call addEntry() or addEntries() or addStyleEntry() or copyFiles() or addPlugin() at least once - otherwise... there is nothing to webpack!');
         }
     }
 

test/config/validator.js

@@ -24,6 +24,8 @@ function createConfig() {
 }
 
 describe('The validator function', () => {
+    function CustomPlugin1() {}
+
     it('throws an error if there are no entries', () => {
         const config = createConfig();
         config.publicPath = '/';
@@ -47,6 +49,17 @@ describe('The validator function', () => {
         expect(Object.keys(config.copyFilesConfigs).length).to.equal(1);
     });
 
+    it('should accept use with addPlugin() only', () => {
+        const config = createConfig();
+        config.setOutputPath('/tmp');
+        config.setPublicPath('/tmp');
+        config.addPlugin(new CustomPlugin1());
+
+        expect(() => {
+            validator(config);
+        }).not.throw();
+    });
+
     it('throws an error if there is no output path', () => {
         const config = createConfig();
         config.publicPath = '/';