fix: host can't be null or empty string

lib/options.json

@@ -375,14 +375,8 @@
       "description": "When using the HTML5 History API, the index.html page will likely have to be served in place of any 404 responses. https://webpack.js.org/configuration/dev-server/#devserverhistoryapifallback"
     },
     "host": {
-      "anyOf": [
-        {
-          "type": "string"
-        },
-        {
-          "type": "null"
-        }
-      ],
+      "type": "string",
+      "minLength": 1,
       "description": "Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
     },
     "hot": {

lib/utils/DevServerPlugin.js

@@ -50,7 +50,7 @@ class DevServerPlugin {
       host = options.webSocketServer.options.host;
     }
     // The `host` option is specified
-    else if (typeof this.options.host !== 'undefined' && this.options.host) {
+    else if (typeof this.options.host !== 'undefined') {
       host = this.options.host;
     }
     // The `port` option is not specified

test/__snapshots__/validate-options.test.js.snap.webpack4

@@ -190,14 +190,22 @@ exports[`options validate should throw an error on the "historyApiFallback" opti
       object { … }"
 `;
 
+exports[`options validate should throw an error on the "host" option with '' value 1`] = `
+"ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
+ - configuration.host should be an non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
+`;
+
 exports[`options validate should throw an error on the "host" option with 'false' value 1`] = `
 "ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
- - configuration.host should be one of these:
-   string | null
-   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost
-   Details:
-    * configuration.host should be a string.
-    * configuration.host should be a null."
+ - configuration.host should be a non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
+`;
+
+exports[`options validate should throw an error on the "host" option with 'null' value 1`] = `
+"ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
+ - configuration.host should be a non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
 `;
 
 exports[`options validate should throw an error on the "hot" option with '' value 1`] = `

test/__snapshots__/validate-options.test.js.snap.webpack5

@@ -190,14 +190,22 @@ exports[`options validate should throw an error on the "historyApiFallback" opti
       object { … }"
 `;
 
+exports[`options validate should throw an error on the "host" option with '' value 1`] = `
+"ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
+ - configuration.host should be an non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
+`;
+
 exports[`options validate should throw an error on the "host" option with 'false' value 1`] = `
 "ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
- - configuration.host should be one of these:
-   string | null
-   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost
-   Details:
-    * configuration.host should be a string.
-    * configuration.host should be a null."
+ - configuration.host should be a non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
+`;
+
+exports[`options validate should throw an error on the "host" option with 'null' value 1`] = `
+"ValidationError: Invalid configuration object. Object has been initialized using a configuration object that does not match the API schema.
+ - configuration.host should be a non-empty string.
+   -> Specify a host to use. If you want your server to be accessible externally. https://webpack.js.org/configuration/dev-server/#devserverhost"
 `;
 
 exports[`options validate should throw an error on the "hot" option with '' value 1`] = `

test/server/host-option.test.js

@@ -78,37 +78,6 @@ describe('host option', () => {
     afterAll(testServer.close);
   });
 
-  describe('is null', () => {
-    beforeAll((done) => {
-      server = testServer.start(
-        config,
-        {
-          static: {
-            directory: staticDirectory,
-            watch: false,
-          },
-          host: null,
-          port,
-        },
-        done
-      );
-      req = request(server.app);
-    });
-
-    it('server address', () => {
-      const address = server.server.address();
-
-      expect(address.address).toBe('::');
-      expect(address.port).toBe(port);
-    });
-
-    it('Request to index', (done) => {
-      req.get('/').expect(200, done);
-    });
-
-    afterAll(testServer.close);
-  });
-
   describe('is 127.0.0.1 (IPv4)', () => {
     beforeAll((done) => {
       server = testServer.start(

test/validate-options.test.js

@@ -175,8 +175,8 @@ const tests = {
     failure: [''],
   },
   host: {
-    success: ['', 'localhost', '::', '::1', null],
-    failure: [false],
+    success: ['localhost', '::', '::1'],
+    failure: [false, '', null],
   },
   hot: {
     success: [true, 'only'],