From 70272f3c369f74c64bb0a535f5a6eb15253685a4 Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Tue, 25 Jul 2017 17:40:40 +0200
Subject: [PATCH] server: Fix crash on missing cache entries

Test for nullptr before constructing std::string.
---
 Source/cmServerProtocol.cxx | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Source/cmServerProtocol.cxx b/Source/cmServerProtocol.cxx
index defba7726f..c5b7f6064a 100644
--- a/Source/cmServerProtocol.cxx
+++ b/Source/cmServerProtocol.cxx
@@ -284,7 +284,9 @@ static bool testValue(cmState* state, const std::string& key,
                       std::string& value, const std::string& keyDescription,
                       std::string* errorMessage)
 {
-  const std::string cachedValue = std::string(state->GetCacheEntryValue(key));
+  const char* entry = state->GetCacheEntryValue(key);
+  const std::string cachedValue =
+    entry == nullptr ? std::string() : std::string(entry);
   if (!cachedValue.empty() && !value.empty() && cachedValue != value) {
     setErrorMessage(errorMessage, std::string("\"") + key +
                       "\" is set but incompatible with configured " +