I want to change the property of an existing `CheckBox` object in my code:

```
string checkBoxName = "checkBox" + Convert.ToString(index);    
Object objCheckBox = checkBoxName;    
CheckBox myCheckBox = objCheckBox as CheckBox;

if (words[1] == "-1")
{
    myCheckBox.Checked = false;
}
else
{
    myCheckBox.Checked = true;
}

```

The code snippet above did not cause a compile error but caused a runtime error as 

> 
> Object reference not set to an instance of an object.
> 
> 
> 

What should I do?