Hello,

 To solve this problem, you will have to set the nullText property on the editor. 

<igDP:Field Name="Department" Label="Department">
                            <igDP:Field.Settings>
                                <igDP:FieldSettings>
                                    <igDP:FieldSettings.EditorStyle>
                                        <Style TargetType="{x:Type igEditors:XamNumericEditor}">
                                            <Setter Property="NullText" Value="N.A"></Setter>
                                        </Style>
                                    </igDP:FieldSettings.EditorStyle>
                                </igDP:FieldSettings>
                            </igDP:Field.Settings>
                        </igDP:Field>

If you want to do it in code, you can do the following:

Style s = new Style(typeof(XamNumericEditor));
s.Setters.Add(new Setter(XamNumericEditor.NullTextProperty,"N.A"));
this.XamDataGrid1.FieldLayouts[0].Fields["Department"].Settings.EditorStyle = s;

Hope this helps.

Remember, if you are bound to a collection of objects, the double will have to be nullable or else you will not be able to blank out the values upon editiing them.