I am writing following code:

```
_normDoc = value as NormDoc;
  if(_normDoc != null)
   {
     ucRusKazTextBoxesAnnotation.Controls["tbNameRu"].Text = _normDoc.AddInfoRu ?? string.Empty;
   }

```

I think that if `_normDoc.AddInfoRu == null` then `ucRusKazTextBoxesAnnotation.Controls["tbNameRu"].Text` will be equal empty string.  

 But I am got error: `NullReferenceException`.
Can you explain me why?

PS. ucRusKazTextBoxesAnnotation not equal null;

**EDIT**: Sorry, I find error, yes, tbNameRu not found, because they are inside Panel control.