Add support for `empty` YANG leaf type

Change-Id: I87eafae9df9accdaa4579ace769996e70da6cb1c
diff --git a/src/libyang_utils.cpp b/src/libyang_utils.cpp
index ddb3630..2669151 100644
--- a/src/libyang_utils.cpp
+++ b/src/libyang_utils.cpp
@@ -31,6 +31,8 @@
         return identityRef_{value->ident()->module()->name(), value->ident()->name()};
     case LY_TYPE_BINARY:
         return binary_{value->binary()};
+    case LY_TYPE_EMPTY:
+        return empty_{};
     case LY_TYPE_DEC64:
     {
         auto v = value->dec64();