commit https://github.com/vim/vim/commit/385111bd86e0b38667879c3e89506ca1ae98e1df Author: Bram Moolenaar <Bram@vim.org> Date: Sat Mar 12 19:23:00 2016 +0100 patch 7.4.1547 Problem: Getting a cterm highlight attribute that is not set results in the string "-1". Solution: Return an empty string. (Taro Muraoka)

TYPEMAP
VIWIN	T_VIOBJNOMUNGE
VIBUF	T_VIOBJNOMUNGE

INPUT
T_VIOBJNOMUNGE
	if (sv_isa($arg, \"${ntype}\")) {
	    IV tmp = SvIV((SV*)SvRV($arg));
	    $var = INT2PTR($type, tmp);
	    if (!tmp)
		croak(\"$ntype no longer exists\");
	}
	else
	    croak(\"$var is not of type ${ntype}\")