fixed bug in runtime where null pointer was counted as match

Author: doczir

runtime/Localsearch_Runtime/Viatra/Query/Operations/Extend/NavigateAssociation.h

@@ -69,11 +69,35 @@ inline NavigateSingleAssociation<SrcType, TrgType, Member, MatchingFrame>::Navig
         ExtendOperation<TrgType, std::list<TrgType>, MatchingFrame>(bindMember), _getSrc(getSrc), _navigate(navigate) {
 }
 
+/**
+ * @brief Nullptr checker utility.
+ *
+ * This helper struct allows the checking for a nullptr regardless if the type is a pointer. Returns false for
+ * non pointer values (as they can never be nullptr).
+ *
+ * @tparam T Type of the parameter.
+ */
+template<class T>
+struct is_null {
+	static bool check(const T) {
+		return false;
+	}
+};
+
+template<class T>
+struct is_null<T*> {
+	static bool check(const T* val) {
+		return val == nullptr;
+	}
+};
+
 template<class SrcType, class TrgType, class Member, class MatchingFrame>
 inline void NavigateSingleAssociation<SrcType, TrgType, Member, MatchingFrame>::on_initialize(MatchingFrame& frame,
         const Matcher::ISearchContext&) {
     _objectHolder.clear();
-    _objectHolder.push_back(static_cast<Member*>(frame.*_getSrc)->*_navigate);
+	auto target = static_cast<Member*>(frame.*_getSrc)->*_navigate;
+	if(!is_null<decltype(target)>::check(target))
+		_objectHolder.push_back(target);
     ExtendOperation<TrgType, std::list<TrgType>, MatchingFrame>::set_data(_objectHolder.begin(), _objectHolder.end());
 }