LINQ Need help to solve System.Reflection.TargetInvocationException error

[RobinsonFrancis (Robin Francis)]

I have an created a LINQ query which goes like this:

For Each rw As DataRow In dt2.Rows
rw("Comments") = (From row In dt1 Where row("INPUT FILENAME").ToString = rw("input_extern_file_name").ToString Select x = row)(0)("A NUMBER").ToString
Next rw

Both dt2 and dt1 are passed in as an argument to a Invoke Code activity where the LINQ is written. There are two tables dt2 refers to this Excel:

dt1 refers to

I was trying to find the the input_extern_file_name in dt2 in dt1’s INPUT FILENAME column, if found I the file name in input_extern_file_name in dt2 in dt1’s INPUT FILENAME column, I want to update the Comments column with the value from A NUMBER column in dt1.
NOTES: Some may notice that it is similar to another query found in one of the other posts. Yes this a modification of that query. If my query is wrong please help me to correct it.
Now back to original question, I am tried running this query in this code:

SearchForMissingFiles.xaml (7.9 KB)
However I am getting this error message:

Source: Invoke code

Message: Exception has been thrown by the target of an invocation.

Exception Type: System.Reflection.TargetInvocationException

RemoteException wrapping System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.  ---> RemoteException wrapping System.NullReferenceException: Object reference not set to an instance of an object. 
   at UiPathCodeRunner_5fd1c3541ac447008c65339fa3541398.Run(DataTable& dt2, DataTable dt1)
	--- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
   at UiPath.Activities.System.Utilities.InvokeCode.CompilerRunner.Run(Object[] args)
   at UiPath.Activities.System.Utilities.InvokeCode.NetCodeInvoker.Run(String userCode, List`1 inArgs, IEnumerable`1 imps, Object[] args)
   at UiPath.Core.Activities.InvokeCode.Execute(CodeActivityContext context)
   at System.Activities.CodeActivity.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager)
   at System.Activities.ActivityInstance.Execute(ActivityExecutor executor, BookmarkManager bookmarkManager)
   at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation)

Kindly help me to fix my linq query.
Thank you.

[ptrobot]

You didn’t consider the case where there’s no match. In those cases you would assign a value from a null row which won’t work.

Dim matchedRow As DataRow

For Each rw As DataRow In dt2.Rows
	matchedRow = (From row In dt1 Where row("INPUT FILENAME").ToString = rw("input_extern_file_name").ToString Select x = row).FirstOrDefault
	If (matchedRow IsNot Nothing) Then
		rw("Comments") = matchedRow("A NUMBER").ToString
	End If
Next rw