diff --git a/MySqlPlus/MySqlSessionCache.cs b/MySqlPlus/MySqlSessionCache.cs
index 783510d..e5a478c 100644
--- a/MySqlPlus/MySqlSessionCache.cs
+++ b/MySqlPlus/MySqlSessionCache.cs
@@ -102,6 +102,9 @@ namespace MontoyaTech.MySqlPlus
         /// <param name="connectionStr"></param>
         public static void Start(string connectionStr)
         {
+            if (string.IsNullOrWhiteSpace(connectionStr))
+                throw new ArgumentException($"{nameof(connectionStr)} cannot be null or empty.");
+
             ConnectionString = connectionStr;
 
             lock (Sessions)