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POLeft outer join with null LINQ exception with Guids
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  1. POLeft outer join with null LINQ exception with Guids
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    copied!<p>I am trying to do a left outer join with null in linq over a List, so if I have one list with {1,2,3,4} and other with {1,2,3,5}, I want the {4}.</p> <p><img src="https://i.stack.imgur.com/qWeD6.png" alt="enter image description here"></p> <pre><code>IEnumerable&lt;AlertChangeSet&gt; listToClear = from a in AlertsCached join b in loadedAlerts on a.AlertId equals b.AlertId into c from b in c.DefaultIfEmpty() select new AlertChangeSet() { AlertId = b.AlertId == Guid.Empty ? a.AlertId : Guid.Empty }; if (listToClear.Any()) { foreach (AlertChangeSet alertChangeSet in listToClear) { Guid a = alertChangeSet.AlertId; //SystemMonitoringService.ClearAlertAsync(alertChangeSet.AlertId.ToString(), null); } } </code></pre> <p>When I run this code, I get this exception:</p> <blockquote> <p>Test method Tgw.Systems.Alerting.Server.Test.ConfigurationTests.UpdateCacheWith2recordsSameIdWorking threw exception: System.NullReferenceException: Object reference not set to an instance of an object. at Tgw.Wcs.Alerting.MonitoringAddIn.Oms.Wcf.OmsWcfSystemMonitor.b__c(&lt;>f__AnonymousType0<code>2 &lt;&gt;h__TransparentIdentifier2, AlertChangeSet b) in OmsWcfSystemMonitor.cs: line 255 at System.Linq.Enumerable.&lt;SelectManyIterator&gt;d__31</code>3.MoveNext() at Tgw.Wcs.Alerting.MonitoringAddIn.Oms.Wcf.OmsWcfSystemMonitor.UpdateAlertsFromCache(IList`1 loadedAlerts) in OmsWcfSystemMonitor.cs: line 275 at Tgw.Systems.Alerting.Server.Test.ConfigurationTests.UpdateCacheWith2recordsSameIdWorking() in ConfigurationTests.ServerCoreTests.cs: line 243</p> </blockquote> <p>I think the problem is the Guid!</p>
 

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