clang-tidy: fix `modernize-use-nullptr` lints
diff --git a/Source/CPack/WiX/cmCPackWIXGenerator.cxx b/Source/CPack/WiX/cmCPackWIXGenerator.cxx
index 0dd7760..1f55b80 100644
--- a/Source/CPack/WiX/cmCPackWIXGenerator.cxx
+++ b/Source/CPack/WiX/cmCPackWIXGenerator.cxx
@@ -63,8 +63,9 @@
   std::string output;
 
   int returnValue = 0;
-  bool status = cmSystemTools::RunSingleCommand(
-    command, &output, &output, &returnValue, 0, cmSystemTools::OUTPUT_NONE);
+  bool status =
+    cmSystemTools::RunSingleCommand(command, &output, &output, &returnValue,
+                                    nullptr, cmSystemTools::OUTPUT_NONE);
 
   cmsys::ofstream logFile(logFileName.c_str(), std::ios::app);
   logFile << command << std::endl;
@@ -665,7 +666,7 @@
 {
   for (auto const& i : ComponentGroups) {
     cmCPackComponentGroup const& group = i.second;
-    if (group.ParentGroup == 0) {
+    if (group.ParentGroup == nullptr) {
       featureDefinitions.EmitFeatureForComponentGroup(group, *this->Patch);
     }
   }
diff --git a/Source/CPack/WiX/cmWIXAccessControlList.cxx b/Source/CPack/WiX/cmWIXAccessControlList.cxx
index cdb86c3..0ebe2f4 100644
--- a/Source/CPack/WiX/cmWIXAccessControlList.cxx
+++ b/Source/CPack/WiX/cmWIXAccessControlList.cxx
@@ -102,7 +102,7 @@
     "Write",
     "WriteAttributes",
     "WriteExtendedAttributes",
-    0
+    nullptr
   };
 
   size_t i = 0;