[BUGFIX] Debugger now respects possible occurence of Closures
A trial isset() call for a property of a Closure resulted in a PHP
error saying "Closure objects cannot have properties". To avoid this,
the isset() statement has been replaced with a property_exists().
This is considered slower than isset(), like claimed in a User Contributed
Note , but obviously the only workaround for these cases . And speed
is not an issue when the debugger is used…