From c39a117161c7977fa6b27be3f1e5696f2f6f35e9 Mon Sep 17 00:00:00 2001
From: albert-github <albert.tests@gmail.com>
Date: Thu, 4 Mar 2021 18:03:41 +0100
Subject: Problems generating chm documentation

Generating doxygen's own manual in chm mode crashed (`qmake doc s_chm`). The problem was introduced during:
Refactoring: replace QRegExp by std::regex in htmlhelp.cpp  (1d993b03f)

Looks like that a std::string cannot add a null pointer to a std::string
---
 src/htmlhelp.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/htmlhelp.cpp b/src/htmlhelp.cpp
index 3d88e4f..d34c8d3 100644
--- a/src/htmlhelp.cpp
+++ b/src/htmlhelp.cpp
@@ -161,7 +161,15 @@ void HtmlHelpIndex::addItem(const char *level1,const char *level2,
   {
     return;
   }
-  std::string key_anchor = key+anchor;
+  std::string key_anchor;
+  if (anchor)
+  {
+    key_anchor = key+anchor;
+  }
+  else
+  {
+    key_anchor = key;
+  }
   m_map.add(key_anchor.c_str(),key.c_str(),url,anchor,hasLink,reversed);
 }
 
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