Fix null reference issue in Get-AzPolicyState

Author: cormacpayne

src/PolicyInsights/PolicyInsights/ChangeLog.md

@@ -18,6 +18,8 @@
         - Additional information about change #1
 -->
 ## Upcoming Release
+* Fix null reference issue in Get-AzPolicyState
+    - More information here: https://github.com/Azure/azure-powershell/issues/9446
 
 ## Version 1.1.1
 * Fix Null reference issue in Get-AzPolicyEvent

src/PolicyInsights/PolicyInsights/Models/PolicyState.cs

@@ -182,7 +182,7 @@ public PolicyState(Management.PolicyInsights.Models.PolicyState policyState)
                 return;
             }
 
-            this.AdditionalProperties = policyState.AdditionalProperties;
+            this.AdditionalProperties = policyState.AdditionalProperties ?? new Dictionary<string, object>();
             this.AdditionalProperties.Remove("@odata.id");
 
             this.Timestamp = policyState.Timestamp;