untraceable uninit warnings

[Graham Barr]

Does anyone have any idea what could be causing 

Use of uninitialized value at PerlHandler subroutine `VC::Delivery::Cycle::handler' 
line 1.

to appear in the errorlog ?

I even added

local $SIG{__WARN__} = sub { warn "here" };

as the first line of VC::Delivery::Cycle::handler, but it never gets
triggered, so it would seem the uninit is before the sub is called.

The strange thing is that it is only this one handler that causes
such a warning, all others are fine.

Thanks,
Graham.