Excel: ListObject can't write into a data-bound object's Nullable<int> columns.

Question

I have a VSTO 4 (Visual Studio 2010) document-level Excel 2007 add-in where I use a ListObject to display data I retrieve from a WCF web service, which uses EF to fetch the data from the database. Some of the columns are Nullable<int> (as the database column is defined with NULL, and EF maps DBNull to null), and those that have null are correctly displayed as an empty cell in the ListObject.

The problem arises when I try to change the value of a cell that is mapped to a Nullable<int> to null by deleting the cell's content - it immediately reverts it to the previous value (and fires the OriginalDataRestored event). IntelliTrace tells me that underneath an exception is thrown and caught in VSTO:

System.ArgumentException occurred
Message=Object of type 'System.DBNull' cannot be converted to type 'System.Nullable`1[System.Int32]'.
Source=mscorlib
StackTrace:

mscorlib.dll!System.RuntimeType.TryChangeType(object value, System.Reflection.Binder binder, System.Globalization.CultureInfo culture, bool needsSpecialCast)
mscorlib.dll!System.RuntimeType.CheckValue(object value, System.Reflection.Binder binder, System.Globalization.CultureInfo culture, System.Reflection.BindingFlags invokeAttr)
mscorlib.dll!System.Reflection.MethodBase.CheckArguments(object[] parameters, System.Reflection.Binder binder, System.Reflection.BindingFlags invokeAttr, System.Globalization.CultureInfo culture, System.Signature sig)
System.dll!System.SecurityUtils.MethodInfoInvoke(System.Reflection.MethodInfo method, object target, object[] args) System.dll!System.ComponentModel.ReflectPropertyDescriptor.SetValue(object component, object value) Microsoft.Office.Tools.Excel.Implementation.dll!Microsoft.Office.Tools.Excel.ListObjectImpl.GetCellValue(object item, Microsoft.Office.Interop.Excel.Range dataRange, int rowIndex, int columnIndex, System.ComponentModel.PropertyDescriptor property, ref bool fireCellRestorationEvent, object excelValue, bool inItemAdd)
(more...)

InnerException:

It seems that for some reason the null from empty cell is converted to DBNull, which cannot be assigned into a Nullable. How can I make the ListObject play well with Nullables?