Add support for `empty` YANG leaf type

Change-Id: I87eafae9df9accdaa4579ace769996e70da6cb1c
diff --git a/src/netconf_access.cpp b/src/netconf_access.cpp
index 5fca200..1340332 100644
--- a/src/netconf_access.cpp
+++ b/src/netconf_access.cpp
@@ -82,7 +82,8 @@
 
 void NetconfAccess::setLeaf(const std::string& path, leaf_data_ value)
 {
-    auto node = m_schema->dataNodeFromPath(path, leafDataToString(value));
+    auto lyValue = value.type() == typeid(empty_) ? std::nullopt : std::optional(leafDataToString(value));
+    auto node = m_schema->dataNodeFromPath(path, lyValue);
     doEditFromDataNode(node);
 }