Add support for `empty` YANG leaf type

Change-Id: I87eafae9df9accdaa4579ace769996e70da6cb1c
diff --git a/tests/yang.cpp b/tests/yang.cpp
index 009465b..79bad71 100644
--- a/tests/yang.cpp
+++ b/tests/yang.cpp
@@ -369,9 +369,14 @@
             type leafref {
                 path "../activeMappedPort";
             }
+            type empty;
         }
     }
 
+    leaf dummyLeaf {
+        type empty;
+    }
+
     leaf clockSpeed {
         type int64;
         config false;
@@ -800,6 +805,7 @@
                                 std::make_unique<yang::TypeInfo>(enums)
                         })
                     }},
+                    yang::TypeInfo{yang::Empty{}},
                 }};
             }
 
@@ -844,6 +850,7 @@
                         {"example-schema"s, "obsoleteLeafWithObsoleteType"},
                         {"example-schema"s, "myRpc"},
                         {"example-schema"s, "systemStats"},
+                        {"example-schema"s, "dummyLeaf"},
                         {"example-schema"s, "subLeaf"}};
                 }
 
@@ -893,6 +900,7 @@
                         {"example-schema"s, "clockSpeed"},
                         {"example-schema"s, "deprecatedLeaf"},
                         {"example-schema"s, "direction"},
+                        {"example-schema"s, "dummyLeaf"},
                         {"example-schema"s, "duration"},
                         {"example-schema"s, "ethernet"},
                         {"example-schema"s, "foodDrinkIdentLeaf"},
@@ -951,6 +959,7 @@
                         {boost::none, "/example-schema:deprecatedLeaf"},
                         {boost::none, "/example-schema:direction"},
                         {boost::none, "/example-schema:duration"},
+                        {boost::none, "/example-schema:dummyLeaf"},
                         {boost::none, "/example-schema:foodDrinkIdentLeaf"},
                         {boost::none, "/example-schema:foodIdentLeaf"},
                         {boost::none, "/example-schema:interface/caseEthernet/ethernet"},