Start-AzAutomationRunbook Object ref error (Azure#26924)

* Start-AzAutomationRunbook Object ref error

* Update ChangeLog.md

---------

Co-authored-by: Divyesh Govaerdhanan <[email protected]>
Co-authored-by: Yabo Hu <[email protected]>

Author: 3 people

src/Automation/Automation/ChangeLog.md

@@ -18,6 +18,7 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Fixed Bug: Start-AzAutomationRunbook throws object reference error when the automation account is not available in the subscription 
 * Upgraded nuget package to signed package.
 
 ## Version 1.10.0

src/Automation/Automation/Common/AutomationPSClient.cs

@@ -2158,7 +2158,7 @@ private IDictionary<string, string> ProcessRunbookParameters(string resourceGrou
                     i++;
                 }
             }
-            else
+            else if(runbook != null)
             {
                 runbookParameters = runbook.Parameters.Cast<DictionaryEntry>().ToDictionary(k => k.Key.ToString(), k => (RunbookParameter)k.Value);