• zend_vm_execute.h is a generated file. You need to change zend_vm_def.h and then run zend_vm_gen.php.
• It looks like this issue also exists on PHP-7.4, so we should target that branch instead.
• Rather than allowing NULL returns, we should do basically what you're doing here, but rather than checking for NULL return, check for an empty array (zend_hash_num_elements(ht) == 0).

Looking at this code, we probably should also add some fast-path skips for empty arrays in more places, as currently we'll end up allocating a new copy of an empty array, just to free it again right away. But that's a separate issue...

I've landed a fix in 15443f8 that does the aforementioned check for empty arrays.

Thanks @nikic Can you add a hacktoberfest-accepted label to this issue?

Sure, done!