Null agrument check added

Author: mihirdilip

src/AspNetCore.Authentication.Basic/BasicUtils.cs

@@ -1,16 +1,17 @@
 // Copyright (c) Mihir Dilip. All rights reserved.
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Security.Claims;
 
 namespace AspNetCore.Authentication.Basic
 {
-	/// <summary>
-	/// Utility class.
-	/// </summary>
-	internal static class BasicUtils
+    /// <summary>
+    /// Utility class.
+    /// </summary>
+    internal static class BasicUtils
 	{
 		/// <summary>
 		/// Builds Claims Principal from the provided information. 
@@ -24,8 +25,9 @@ internal static class BasicUtils
 		/// <returns></returns>
 		internal static ClaimsPrincipal BuildClaimsPrincipal(string username, string schemeName, string claimsIssuer, IEnumerable<Claim> claims = null)
 		{
-			var claimsList = new List<Claim>();
+			if (string.IsNullOrWhiteSpace(schemeName)) throw new ArgumentNullException(nameof(schemeName));
 
+			var claimsList = new List<Claim>();
 			if (claims != null) claimsList.AddRange(claims);
 
 			if (!claimsList.Any(c => c.Type == ClaimTypes.NameIdentifier))