Update for some unit tests

Core/Remote/PiscalSshClient.cs

@@ -24,6 +24,8 @@ namespace LeafWeb.Core.Remote
 
 		public PiscalSshClient(string connectionString)
 		{
+            if (string.IsNullOrEmpty(connectionString))
+                throw new ArgumentNullException("connectionString");
 			var conn = new DbConnectionStringBuilder {ConnectionString = connectionString};
 
 			_host = conn["host"] as string;