From 5a770ec85e1abda3783a43bdd7b21cd368811356 Mon Sep 17 00:00:00 2001
From: Olaoluwa Osuntokun <laolu32@gmail.com>
Date: Thu, 27 Apr 2017 21:47:56 -0700
Subject: [PATCH] gcs/builder: an empty filter has a zero-hash

---
 gcs/builder/builder.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gcs/builder/builder.go b/gcs/builder/builder.go
index 5235d5a..b72e14a 100644
--- a/gcs/builder/builder.go
+++ b/gcs/builder/builder.go
@@ -371,6 +371,11 @@ func BuildExtFilter(block *wire.MsgBlock) (*gcs.Filter, error) {
 
 // GetFilterHash returns the double-SHA256 of the filter.
 func GetFilterHash(filter *gcs.Filter) chainhash.Hash {
+	var zero chainhash.Hash
+	if filter == nil {
+		return zero
+	}
+
 	hash1 := chainhash.HashH(filter.NBytes())
 	return chainhash.HashH(hash1[:])
 }