fix(@angular/cli): Add an error message when we call ng doc without keyword. Currently, we open a page with the keyword undefined.

Author: wKoza

packages/angular/cli/commands/doc-impl.ts

@@ -14,13 +14,17 @@ const opn = require('opn');
 
 export class DocCommand extends Command<DocCommandSchema> {
   public async run(options: DocCommandSchema & Arguments) {
-    let searchUrl = `https://angular.io/api?query=${options.keyword}`;
-    if (options.search) {
-      searchUrl = `https://www.google.com/search?q=site%3Aangular.io+${options.keyword}`;
-    }
+    if(options.keyword) {
+      let searchUrl = `https://angular.io/api?query=${options.keyword}`;
+      if (options.search) {
+        searchUrl = `https://www.google.com/search?q=site%3Aangular.io+${options.keyword}`;
+      }
 
-    return opn(searchUrl, {
+      return opn(searchUrl, {
       wait: false,
-    });
+      });
+    }
+    this.logger.error('You should specify a keyword, for instance, `ng doc ActivatedRoute`.');
+    return 0;
   }
 }