From 900e076d215d01f08488126db401b6176539efd1 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Fri, 10 Oct 2008 16:21:50 -0700
Subject: [PATCH] handle zeroed interface in ifaceI2I

R=r
OCL=16938
CL=16938
---
 src/runtime/iface.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/runtime/iface.c b/src/runtime/iface.c
index 089975b923..de59172d17 100644
--- a/src/runtime/iface.c
+++ b/src/runtime/iface.c
@@ -231,7 +231,6 @@ sys·ifaceI2T(Sigt *st, Map *im, void *it, void *ret)
 void
 sys·ifaceI2I(Sigi *si, Map *im, void *it, Map *retim, void *retit)
 {
-
 	if(debug) {
 		prints("I2I sigi=");
 		printsigi(si);
@@ -241,15 +240,17 @@ sys·ifaceI2I(Sigi *si, Map *im, void *it, Map *retim, void *retit)
 	}
 
 	if(im == nil) {
-		throw("ifaceI2I: nil map");
-		return;
+		// If incoming interface is uninitialized (zeroed)
+		// make the outgoing interface zeroed as well.
+		retim = nil;
+		retit = nil;
+	} else {
+		retit = it;
+		retim = im;
+		if(im->sigi != si)
+			retim = hashmap(si, im->sigt);
 	}
 
-	retit = it;
-	retim = im;
-	if(im->sigi != si)
-		retim = hashmap(si, im->sigt);
-
 	if(debug) {
 		prints("I2I ret=");
 		printiface(retim, retit);
-- 
2.48.1