How to resolve Value cannot be null Parameter name source in linq

Question

I don t know why I get this kind of error  It happens sometimes  and I suspicious of my code that still have thread running while I close my Application  So when I open again it happens  Value cannot be null  Parameter name  source StackTree         at System Linq Enumerable Where TSource  IEnumerable 1 source  Func 2 predicate        at Susenas2015 ViewModels Kuesioner VMVsen15 KVal SettingValidationAndRange List 1 listTextBox  List 1 listCheckBox  TabControl tabControl  in d  handita Office Project Susenas 2015 Aplikasi Template Survei Susenas2015 ViewModels Kuesioner VMVsen15 KVal cs line 430       at Susenas2015 ViewModels Kuesioner VMVsen15 KVal vSen15 K Loaded Object sender  RoutedEventArgs e  in d  handita Office Project Susenas 2015 Aplikasi Template Survei Susenas2015 ViewModels Kuesioner VMVsen15 KVal cs line 846       at System Windows RoutedEventHandlerInfo InvokeHandler Object target  RoutedEventArgs routedEventArgs        at System Windows EventRoute InvokeHandlersImpl Object source  RoutedEventArgs args  Boolean reRaised        at System Windows UIElement RaiseEventImpl DependencyObject sender  RoutedEventArgs args        at System Windows UIElement RaiseEvent RoutedEventArgs e        at System Windows BroadcastEventHelper BroadcastEvent DependencyObject root  RoutedEvent routedEvent        at System Windows BroadcastEventHelper BroadcastLoadedEvent Object root        at MS Internal LoadedOrUnloadedOperation DoWork         at System Windows Media MediaContext FireLoadedPendingCallbacks         at System Windows Media MediaContext FireInvokeOnRenderCallbacks         at System Windows Media MediaContext RenderMessageHandlerCore Object resizedCompositionTarget        at System Windows Media MediaContext RenderMessageHandler Object resizedCompositionTarget        at System Windows Media MediaContext Resize ICompositionTarget resizedCompositionTarget        at System Windows Interop HwndTarget OnResize         at System Windows Interop HwndTarget HandleMessage WindowMessage msg  IntPtr wpa   My code here it is     private void SettingValidationAndRange List lt TextBox gt  listTextBox  List lt CheckBox gt  listCheckBox  TabControl tabControl                         List lt string gt  listNotDeclare   new List lt string gt                  foreach  var textB in listTextBox                                if  textB Tag    null                      break                   Metadata metadata   ListMetadataKor Where                      x   gt   quot text quot    x Field    textB Name    this line 430                    FirstOrDefault                     if  metadata    null                                        if   string IsNullOrEmpty textB Name                           listNotDeclare Add textB Name                                     else                                       metadata TabControl   tabControl                      textB Tag   metadata                                     textB AddEvents                    textB AutomateFocus                                if  listNotDeclare Count  gt  0                                Clipboard SetText string Join  quot   quot   listNotDeclare ToArray                      Dialog Info  quot Ada beberapa Metadata tidak ditemukan data sudah dicopy ke clipboard quot                              When I start my application for my first time  it doesn t get any error  It happens when I open in 2nd or more  And if I open my application it would stuck in that code  How I can solve this  I m pretty sure that my Property ListMetadataKor is not null And ListMetadataKor is instance of List lt Metadata gt  object that I have created  It happens only in rare cases  And I don t know to solve it UPDATE This is my code in image I fill ListMetadataKor with this code BWHelper Run  s  e    gt        DataTable dataMetaDataKOR   ExcelHelper GetDataTableFromExcel          AppConstants FILE METADATA  AppConstants SHEET METADATA KOR             DataTable dataKonsistensiKOR   ExcelHelper GetDataTableFromExcel           AppConstants FILE METADATA  AppConstants SHEET KONSISTENSI KOR              listKonsistensiKor   Tools ToolConvert GetKonsistensi dataKonsistensiKOR       listMetadataKor   Tools ToolConvert GetMetadata dataMetaDataKOR        foreach  Metadata metadata in listMetadataKor                metadata Range ProsesRange               s  e    gt        try               kor   new VSEN15 K     Title    quot Validasi Susenas - KOR quot             kor DataContext   new VMVsen15 KVal rtSusenas MasterRT  kor  this  listKonsistensiKor  listMetadataKor           kor PreviewKeyDown    EventsCollection EnterAsTabPreviewKeyDown          vmHome HideLoading            UpdateMetaDataEntriKOR RTSusenas MasterRT           kor ShowDialog              catch  Exception Ex                vmHome HideLoading            Dialog Error Ex              And then I throw the variable through constructor of my class  public VMVsen15 KVal          MasterRT masterRT          VSEN15 K vSen15 K          IDaftarSusenas vmDaftarRTSusenas          List lt Konsistensi gt  listKonsistensiKor          List lt Metadata gt  listMetadataKor                           ListArtDetail   new ObservableCollection lt ARTDetailVal gt              this ListKonsistensiKor   listKonsistensiKor          this ListMetadataKor   listMetadataKor   My tools konsistensi like this public static List lt Konsistensi gt  GetKonsistensi DataTable dataTable        List lt Konsistensi gt  listMetadata   new List lt Konsistensi gt         for  int i   0  i  lt  dataTable Rows Count  i                  Konsistensi k   new Konsistensi            object   required   new object     DBNull Value   quot  quot             k Field   dataTable Rows i  FIELD  ToString            if  string IsNullOrWhiteSpace k Field   continue          k Message   dataTable Rows i  MESSAGE  ToString            var obj   dataTable Rows i  ORDER           k Order    required Contains dataTable Rows i  ORDER     Convert ToInt32 dataTable Rows i  ORDER      int  null          k Page    required Contains dataTable Rows i  PAGE     Convert ToInt32 dataTable Rows i  PAGE      int  null          k Perlakuan   dataTable Rows i  PERLAKUAN  ToString            k RelFields   dataTable Rows i  RELFIELDS  ToString            k Rule   dataTable Rows i  RULE  ToString             if  dataTable Rows i  LEVEL  ToString   ToUpper        quot ART quot                k LevelKonsistensi   LevelKonsistensi ART          else if  dataTable Rows i  LEVEL  ToString   ToUpper        quot RT quot                k LevelKonsistensi   LevelKonsistensi RT          else if  dataTable Rows i  LEVEL  ToString   ToUpper        quot RTWARNING quot                k LevelKonsistensi   LevelKonsistensi RTWarning          else if  dataTable Rows i  LEVEL  ToString   ToUpper   Contains  quot ARTWARNING quot                k LevelKonsistensi   LevelKonsistensi ARTWarning          else             k LevelKonsistensi   LevelKonsistensi Lain             k LevelKonsistensi   dataTable Rows i  LEVEL  ToString   Contains  quot ART quot     LevelKonsistensi ART   LevelKonsistensi RT          if  k IsEmpty                continue           listMetadata Add k             return listMetadata

User · Answer

When you call a Linq statement like this:

// x = new List<string>();
var count = x.Count(s => s.StartsWith("x"));

You are actually using an extension method in the System.Linq namespace, so what the compiler translates this into is:

var count = Enumerable.Count(x, s => s.StartsWith("x"));

So the error you are getting above is because the first parameter, source (which would be x in the sample above) is null.

User · Answer

Error message clearly says that source parameter is null  Source is the enumerable you are enumerating  In your case it is ListMetadataKor object  And its definitely null at the time you are filtering it second time  Make sure you never assign null to this list  Just check all references to this list in your code and look for assignments

User · Answer

System ArgumentNullException  Value cannot be null  Parameter name    value   This error message is not very helpful   You can get this error in many different ways   The error may not always be with the parameter name  value   It could be whatever parameter name is being passed into a function   As a generic way to solve this  look at the stack trace or call stack   Test method GetApiModel threw exception   System ArgumentNullException  Value cannot be null  Parameter name  value     at Newtonsoft Json JsonConvert DeserializeObject String value  Type type  JsonSerializerSettings settings    You can see that the parameter name value is the first parameter for DeserializeObject   This lead me to check my AutoMapper mapping where we are deserializing a JSON string   That string is null in my database   You can change the code to check for null

User · Answer

Value cannot be null    Parameter name  source   Above error comes in situation when you are querying the collection which is null   For demonstration below code will result in such an exception   Console WriteLine  Hello World    IEnumerable lt int gt  list   null  list Where d   gt  d   4  FirstOrDefault      Here is the output of the above code      Hello World   Run-time exception  line 11   Value cannot be null    Parameter name  source      Stack Trace        System ArgumentNullException  Value cannot be null    Parameter name  source  at Program Main    line 11    In your case ListMetadataKor is null  Here is the fiddle if you want to play around

[c#] How to resolve Value cannot be null. Parameter name: source in linq?

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