I have the same problem. When I clear the text in the XamNumericEditor the ConvertBack in the converter specified on the Editor's Value binding is reporting the value as DBNull.

Here's the binding:

Value="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type NS:View}}, Path=Master.CurrentlyEditedItem.NullableDouble, Converter={StaticResource DoubleToPercentage}}"

ValueType="{x:Type System:Double}" Mask="nnn%"

The converter itself actually has input and output of both double it's just multiplying or dividing by 100.

I can fix it by just checking for DBNull along with Null, it's just weird that it would be an issue at all.

Reflector reveals the reason?

[EditorBrowsable(EditorBrowsableState.Never)]

    public bool ConvertDisplayTextToValue(string displayText, out object value, out Exception error)

    {

        error = null;

        value = null;

        try

        {

            value = this.ValueToDisplayTextConverterResolved.ConvertBack(displayText, base.ValueType, this, base.FormatProviderResolved as CultureInfo);

            if (value == null)

            {

                if ((displayText == null) || (displayText.Length == 0))

                {

                    value = DBNull.Value;

                }

                else

                {

                    error = Utils.GetTextToValueConversionError(base.ValueType, displayText);

                    return false;

                }

            }

        }

        catch (Exception exception)

        {

            error = exception;

            return false;

        }

        return true;

    }

I'm not using ClearCellContents command. The DbNull is returned when I clear the content of the field with the backspace key.

The grid is bound to a collection, not to a DataTable.

The type of the field is int, the editor is xamNumericEditor.