Error "Value '' could not be converted."

Question

WPF - MVVM arch.  .Net ver 4.0, VS2010.
I am trying to clear the selection in a comboBox get an error "Value '' could not be converted."
The ComboBox's iItemSource is bound to a key-value pair list.  The SelectedValue is the Key and the DisplayMemberPath is bound to the Value.
If the ItemSource is bound to an ordinary datatype, such as a string, and clear the selected value in ComboBox, this error doesnt occur.  But I needed it as a Key-Value pair since its a lookup. 
Suspect that the error could be because the key-value pair has no corresponding null entry or could not take a null value.  Could this a bug in the framework.  How to resolve this.  Seen the blogs that says use Nullable
value and do the conversion, but doesnt appear to be a good way to resolve this since an explicit conversion adapter have to be written.  Is there a better way to resolve this.

Answer 1

I would have thought
Bind SelectedValue to a nullable property.
That's the key it's going to end up with.
Your key might have to be a nullable type as well.
Set that property to null.
You might also have to do the synchronise thing
IsSynchronizedWithCurrentItem="True"
On the combo.
Hope that helps.
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