some bug fix

app/Http/Controllers/StatisticController.php

@@ -43,7 +43,7 @@ class StatisticController extends Controller
 
             $this->addSystems($result, $task);
 
-            $this->addTags($result, $task, $tags[$task->id]);
+            $this->addTags($result, $task, $tags[$task->id] ?? []);
         }
 
         return $result;

database/migrations/2020_08_18_085114_create_tags_table.php

@@ -23,8 +23,10 @@ class CreateTagsTable extends Migration
         });
 
         Schema::create('tag_task', function (Blueprint $table) {
+            $table->id();
             $table->unsignedBigInteger('tag_id');
             $table->unsignedBigInteger('task_id');
+            $table->timestamps();
         });
     }