fix null reference and method case insensitive for Invoke-AzRestMethod (#13302)

* fix null reference

* Update InvokeAzRestMethodCommand.cs

* Update ChangeLog.md

* Update ChangeLog.md

Author: VeryEarly

src/Accounts/Accounts/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Fixed null reference and method case insensitive in `Invoke-AzRestMethod`
 * [Breaking Change] Removed `Get-AzProfile` and `Select-AzProfile`
 * Updated Azure.Core to 1.5.1
 

src/Accounts/Accounts/Rest/InvokeAzRestMethodCommand.cs

@@ -108,7 +108,7 @@ public override void ExecuteCmdlet()
                 this.Path = ConstructPath(this.IsParameterBound(c => c.SubscriptionId) ? this.SubscriptionId : context.Subscription.Id, this.ResourceGroupName, this.ResourceProviderName, this.ResourceType, this.Name);
             }
 
-            switch (this.Method)
+            switch (this.Method.ToUpper())
             {
                 case "GET":
                     response = ServiceClient
@@ -197,7 +197,7 @@ private string ConstructPath(string sub, string rg, string rp, string[] types, s
                 for (int i = 0; i < types.Length; i++)
                 {
                     sb.Append(slash + types[i]);
-                    if (i != names.Length)
+                    if (names != null && i != names.Length)
                     {
                         sb.Append(slash + names[i]);
                     }       
@@ -206,4 +206,4 @@ private string ConstructPath(string sub, string rg, string rp, string[] types, s
             return sb.ToString();
         }
     }
-}
+}