sub block(&) {
    return undef;
}

print block {'whatever'} // "is undef";
__END__
String found where operator expected at bug.pl line 6, near "// "is undef""
	(Missing operator before  "is undef"?)
Too many arguments for main::block at bug.pl line 6, near "// "is undef""
syntax error at bug.pl line 6, near "// "is undef""
Execution of bug.pl aborted due to compilation errors.