Description:
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When calling register_shutdown_function with an array argument in which the first index is an unset variable or if the first index is numeric 0 and the second any string variable apache2 crashes...I've tested it on Apache v2.0.52 and v2.0.53.

In the server's error log it says:
[Sat Apr 09 20:37:19 2005] [notice] Parent: child process exited with status 3221225477 -- Restarting.
[Sat Apr 09 20:37:19 2005] [notice] Apache/2.0.53 (Win32) PHP/5.0.4 configured -- resuming normal operations
[Sat Apr 09 20:37:19 2005] [notice] Server built: Feb 10 2005 06:11:34
[Sat Apr 09 20:37:19 2005] [notice] Parent: Created child process 3900
[Sat Apr 09 20:37:19 2005] [notice] Child 3900: Child process is running
[Sat Apr 09 20:37:19 2005] [notice] Child 3900: Acquired the start mutex.
[Sat Apr 09 20:37:19 2005] [notice] Child 3900: Starting 250 worker threads.

Reproduce code:
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unset($obj);
register_shutdown_function(array($obj,""));
register_shutdown_function(array($obj,"some string"));
register_shutdown_function(array(0,""));
register_shutdown_function(array(0,"some string"));