This just makes the error message go away.
Better than flooding the log.
In my opinion one should never attempt to use a variable which might be unitialized. Therefore the error message just hints you about a error. However another fix which allows to leave variable uninitialized would be:
print "blupp " . (defined($bla) ? $bla : '');
This makes it clear to someone else needing to modify the script, that the variable might be undefined.
Regards Michael