I've finally managed to upgrade a WP site from v5.0 to v5.4. The only issue left is when I create an empty functions.php file I get 500 error.

Does someone have an idea why is that? Thanks.

Update: My goal is to place the following into functions.php:

function my_acf_init() {
  acf_update_setting('google_api_key', $_ENV['GOOGLE_MAPS_API_KEY']);

add_action('acf/init', 'my_acf_init');
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    So there was no functions file before and now there is a blank file? Is the functions file at least a valid PHP file? <?php as the first line. – jdm2112 Jul 7 '20 at 17:06
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    Why do you need to do that if it creates an error? – mozboz Jul 7 '20 at 17:21
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    500 errors are just Apache/Nginx's way of saying something in PHP went wrong. Look at the PHP error log for the actual error message – Tom J Nowell Jul 7 '20 at 17:27
  • @jdm2112 My goal isn't to add an empty functions.php obviously. I have gradually removed its content to see where it breaks. I wanna add an add_action call to inject env variable value to Advanced Custom Fields. – haxpanel Jul 8 '20 at 9:02
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    Removing code in pieces to find the offending section is not very efficient. If you are actively developing this site the PHP log is your friend. I have no experience with Heroku but this might help: devcenter.heroku.com/articles/php-logging – jdm2112 Jul 8 '20 at 18:03

I've managed to print the error message by adding the following to the functions.php:

function exception_handler($exception) {
    echo "Uncaught exception: " , $exception->getMessage(), "\n";


For some reason logs did not include the error details before. The error is call to undefined function is_blog_installed() which I have no idea why's that. :D

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