Update Model.php

src/Illuminate/Database/Eloquent/Model.php

@@ -230,7 +230,7 @@ public function fill(array $attributes)
             if ($this->isFillable($key)) {
                 $this->setAttribute($key, $value);
             } elseif ($totallyGuarded) {
-                $model = get_class($this);
+                $model = static::class;
                 throw new MassAssignmentException(
                     "Add [{$key}] to fillable property to allow mass assignment on {$model}."
                 );