Fixed a validation issue in constructor

Author: sesispla

src/KubernetesClientCredentials.cs

@@ -32,7 +32,7 @@ public KubernetesClientCredentials(string userName, string password)
                 throw new ArgumentNullException(nameof(userName));
             }
 
-            if (string.IsNullOrWhiteSpace(userName))
+            if (string.IsNullOrWhiteSpace(password))
             {
                 throw new ArgumentNullException(nameof(password));
             }