clean up Value of XMLDocument

tinyxml2.cpp

@@ -645,6 +645,9 @@ XMLNode::~XMLNode()
 
 const char* XMLNode::Value() const 
 {
+    // Catch an edge case: XMLDocuments don't have a a Value. Carefully return nullptr.
+    if ( this->ToDocument() )
+        return 0;
     return _value.GetStr();
 }