fix: ensure Data is initialized with default value on empty Consul response

Author: AlphaYu

src/Infrastructures/Consul/Configuration/DefaultConsulConfigurationProvider.cs

@@ -23,7 +23,10 @@ private void LoadData(QueryResult<KVPair> queryResult)
             || queryResult.Response.Value == null
             || queryResult.Response.Value.Length == 0)
         {
-            Data = new Dictionary<string, string?>();
+            Data = new Dictionary<string, string?>()
+            {
+                { "nullContent",""}
+            };
             return;
         }
         Stream stream = new MemoryStream(queryResult.Response.Value);