Magento 2-从自定义架构创建db表时出错

<?php
namespace Vendor\Module\Setup;

use Magento\Framework\Setup\InstallSchemaInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\SchemaSetupInterface;

class InstallSchema implements InstallSchemaInterface
{
    public function install(SchemaSetupInterface $setup, ModuleContextInterface $context)
    {
        $installer = $setup;
        $installer->startSetup();

        $table = $installer->getConnection()->newTable(
            $installer->getTable('custom_table')
        )->addColumn(
            'id',
            \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
            null,
            ['identity' => true, 'unsigned' => true, 'nullable' => false, 'primary' => true],
            'ID'
        )->addColumn(
            'name',
            \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
            255,
            ['nullable' => false],
            'Name'
        )->addColumn(
            'created_at',
            \Magento\Framework\DB\Ddl\Table::TYPE_TIMESTAMP,
            null,
            ['nullable' => false, 'default' => \Magento\Framework\DB\Ddl\Table::TIMESTAMP_INIT],
            'Created At'
        )->setComment(
            'Custom Table'
        );

        $installer->getConnection()->createTable($table);
        $installer->endSetup();
    }
}