Fix null ref in generated cmdlets when context is not set

src/Accounts/Accounts/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Display user friendly error message when context is null in Az 4.0
 
 ## Version 1.6.4
 * Add a deprecation message for `Resolve-Error` alias.

src/Accounts/Accounts/CommonModule/ContextAdapter.cs

@@ -170,6 +170,11 @@ namespace Microsoft.Azure.Commands.Common
         /// <returns></returns>
         internal async Task AuthorizeRequest(IAzureContext context, string resourceId, HttpRequestMessage request, CancellationToken outerToken)
         {
+            if (context == null || context.Account == null || context.Environment == null)
+            {
+                throw new InvalidOperationException(Resources.InvalidAzureContext);
+            }
+
             await Task.Run(() =>
             {
                 resourceId = context?.Environment?.GetAudienceFromRequestUri(request.RequestUri) ?? resourceId;

src/Accounts/Accounts/Properties/Resources.Designer.cs

@@ -483,6 +483,15 @@ namespace Microsoft.Azure.Commands.Profile.Properties {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to The context is invalid. Please login using Connect-AzAccount..
+        /// </summary>
+        internal static string InvalidAzureContext {
+            get {
+                return ResourceManager.GetString("InvalidAzureContext", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Endpoint provided is invalid. Please check the value and retry again with the correct value..
         /// </summary>

src/Accounts/Accounts/Properties/Resources.resx

@@ -465,4 +465,7 @@
   <data name="SovereignProfileDescription" xml:space="preserve">
     <value>A snapshot of the service API versiosn available in Azure Sovereign Clouds and the Azure Global Cloud.</value>
   </data>
+  <data name="InvalidAzureContext" xml:space="preserve">
+    <value>The context is invalid. Please login using Connect-AzAccount.</value>
+  </data>
 </root>