From 71b9e59c5af147120ae379df771ee1fb9490f9af Mon Sep 17 00:00:00 2001
From: jl777 <jameslee777@yahoo.com>
Date: Thu, 22 Feb 2018 12:00:08 +0200
Subject: [PATCH] Guard against set generate  crash in regtest

---
 src/main.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/main.cpp b/src/main.cpp
index 72f25f1fc..99d66f4a2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4216,7 +4216,9 @@ void static CheckBlockIndex()
     // Build forward-pointing map of the entire block tree.
     std::multimap<CBlockIndex*,CBlockIndex*> forward;
     for (BlockMap::iterator it = mapBlockIndex.begin(); it != mapBlockIndex.end(); it++) {
-        forward.insert(std::make_pair(it->second->pprev, it->second));
+        if ( it != 0 && it->second != 0 )
+            forward.insert(std::make_pair(it->second->pprev, it->second));
+        else break;
     }
 
     assert(forward.size() == mapBlockIndex.size());