我想在中放置一些自定义代码functions.php 这是我无法做到的。为什么我在创建后会出现以下错误（即使是空的）functions.php? 我正在使用WP 5.4.2Heroku-wp?

Fatal error: Uncaught Error: Call to undefined function is_blog_installed() in /app/public.built/wp-includes/load.php:606 Stack trace: #0 /app/public.built/wp-settings.php(161): wp_not_installed() #1 /app/public.built/wp-config.php(255): require_once(\'/app/public.bui...\') #2 /app/public.built/wp-load.php(37): require_once(\'/app/public.bui...\') #3 /app/public.built/wp-blog-header.php(13): require_once(\'/app/public.bui...\') #4 /app/public.built/index.php(17): require(\'/app/public.bui...\') #5 {main} thrown in /app/public.built/wp-includes/load.php on line 606

Fatal error: Uncaught Error: Call to undefined function get_option() in /app/public.built/wp-includes/l10n.php:69 Stack trace: #0 /app/public.built/wp-includes/l10n.php(136): get_locale() #1 /app/public.built/wp-includes/l10n.php(756): determine_locale() #2 /app/public.built/wp-includes/class-wp-fatal-error-handler.php(41): load_default_textdomain() #3 [internal function]: WP_Fatal_Error_Handler->handle() #4 {main} thrown in /app/public.built/wp-includes/l10n.php on line 69