set_property: Fix crash when setting LINK_LIBRARIES to nothing

We use a special dedicated structure to store the LINK_LIBRARIES target
property.  Do not try to construct a string from a NULL value.  Instead
leave the property structure empty when no value is given.

Reported-by: Ghyslain Leclerc <ghleclerc@gmail.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 70005b4..2d34747 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -1748,9 +1748,12 @@ void cmTarget::SetProperty(const std::string& prop, const char* value)
   else if (prop == "LINK_LIBRARIES")
     {
     this->Internal->LinkImplementationPropertyEntries.clear();
-    cmListFileBacktrace lfbt = this->Makefile->GetBacktrace();
-    cmValueWithOrigin entry(value, lfbt);
-    this->Internal->LinkImplementationPropertyEntries.push_back(entry);
+    if (value)
+      {
+      cmListFileBacktrace lfbt = this->Makefile->GetBacktrace();
+      cmValueWithOrigin entry(value, lfbt);
+      this->Internal->LinkImplementationPropertyEntries.push_back(entry);
+      }
     }
   else if (prop == "SOURCES")
     {
@@ -1834,9 +1837,12 @@ void cmTarget::AppendProperty(const std::string& prop, const char* value,
     }
   else if (prop == "LINK_LIBRARIES")
     {
-    cmListFileBacktrace lfbt = this->Makefile->GetBacktrace();
-    cmValueWithOrigin entry(value, lfbt);
-    this->Internal->LinkImplementationPropertyEntries.push_back(entry);
+    if (value)
+      {
+      cmListFileBacktrace lfbt = this->Makefile->GetBacktrace();
+      cmValueWithOrigin entry(value, lfbt);
+      this->Internal->LinkImplementationPropertyEntries.push_back(entry);
+      }
     }
   else if (prop == "SOURCES")
     {