Description: When binding to a null value, the RadSpinEditor throws an exception. This missing functionality is also noticed with the standard Windows Numeric Up Down control.

How to reproduce:
- add a RadSpinEditor and two RadButtons;
- use the following code:

public partial class Form1 : Form
{
    private BindingSource _bindActiveObject = new BindingSource { DataSource = typeof(MyBindingObject) };

    public Form1()
    {
        InitializeComponent();

        this.radSpinEditor1.DataBindings.Add(new Binding("Value", _bindActiveObject, "MyValue"));
    }

    private void radButton1_Click(object sender, EventArgs e)
    {
        _bindActiveObject.DataSource = new MyBindingObject { MyValue = Convert.ToDouble(100) };
    }

    private void radButton2_Click(object sender, EventArgs e)
    {
        _bindActiveObject.DataSource = new MyBindingObject { MyValue = null };
    }
}

public class MyBindingObject
{
    private decimal? _myValue;

    public decimal? MyValue
    {
        get
        {
            return _myValue;
        }
        set
        {
            _myValue = value;
        }
    }
}

Workaround:

Use the following custom RadSpinEditor:

private BindingSource _bindActiveObject = new BindingSource { DataSource = typeof(MyBindingObject) };

public Form1()
{
    InitializeComponent();
    this.radSpinEditor1.NullableValueChanged += Form1_NullableValueChanged;
    this.radSpinEditor1.DecimalPlaces = 2;
    this.radSpinEditor1.DataBindings.Add(new Binding("NullableValue", _bindActiveObject,
        "MyValue", true, DataSourceUpdateMode.OnPropertyChanged));
}

private void Form1_NullableValueChanged(object sender, EventArgs e)
{
    Console.WriteLine("NullableValue = " + this.radSpinEditor1.NullableValue + "");
}

private void radButton1_Click(object sender, EventArgs e)
{
    MyBindingObject obj = new MyBindingObject { MyValue = 65.45m };
    _bindActiveObject.DataSource = obj; 
}

private void radButton2_Click(object sender, EventArgs e)
{
    _bindActiveObject.DataSource = new MyBindingObject { MyValue = null };
}

public class MyBindingObject
{
    private decimal? _myValue;

    public decimal? MyValue
    {
        get
        {
            return _myValue;
        }
        set
        {
            _myValue = value;
        }
    }
}

public class MySpinEditor : RadSpinEditor
{
    public event EventHandler NullableValueChanged;

    public decimal? NullableValue
    {
        get
        {
            return (this.SpinElement as MySpinEditorElement).NullableValue;
        }
        set
        {
            (this.SpinElement as MySpinEditorElement).NullableValue = value;
        }
    }

    public MySpinEditor()
    {
        this.AutoSize = true;
        this.TabStop = false;
        base.SetStyle(ControlStyles.Selectable, true);
    }

    protected override void CreateChildItems(RadElement parent)
    {
        Type baseType = typeof(RadSpinEditor);
        MySpinEditorElement element = new MySpinEditorElement();
        element.RightToLeft = this.RightToLeft == System.Windows.Forms.RightToLeft.Yes;
        this.RootElement.Children.Add(element);

        element.ValueChanging += spinElement_ValueChanging;
        element.ValueChanged += spinElement_ValueChanged;
        element.TextChanging += spinElement_TextChanging;
        element.NullableValueChanged += element_NullableValueChanged;

        element.KeyDown += OnSpinElementKeyDown;
        element.KeyPress += OnSpinElementKeyPress;
        element.KeyUp += OnSpinElementKeyUp;

        baseType.GetField("spinElement", BindingFlags.Instance | BindingFlags.NonPublic).SetValue(this, element);
    }

    void element_NullableValueChanged(object sender, EventArgs e)
    {
        if (this.NullableValueChanged != null)
        {
            this.NullableValueChanged(this, EventArgs.Empty);
        }
    }

    private Dictionary<string, MethodInfo> cache = new Dictionary<string, MethodInfo>();

    private void InvokeBaseMethod(string name, params object[] parameters)
    {
        if (!cache.ContainsKey(name))
        {
            cache[name] = typeof(RadSpinEditor).GetMethod(name, BindingFlags.Instance | BindingFlags.NonPublic);
        }

        cache[name].Invoke(this, parameters);
    }

    private void OnSpinElementKeyUp(object sender, KeyEventArgs e)
    {
        this.InvokeBaseMethod("OnSpinElementKeyUp", sender, e);
    }

    private void OnSpinElementKeyPress(object sender, KeyPressEventArgs e)
    {
        this.InvokeBaseMethod("OnSpinElementKeyPress", sender, e);
    }

    private void OnSpinElementKeyDown(object sender, KeyEventArgs e)
    {
        this.InvokeBaseMethod("OnSpinElementKeyDown", sender, e);
    }

    private void spinElement_TextChanging(object sender, TextChangingEventArgs e)
    {
        this.InvokeBaseMethod("spinElement_TextChanging", sender, e);
    }

    private void spinElement_ValueChanged(object sender, EventArgs e)
    {
        this.InvokeBaseMethod("spinElement_ValueChanged", sender, e);
        this.NullableValue = this.Value;
    }

    private void spinElement_ValueChanging(object sender, ValueChangingEventArgs e)
    {
        this.InvokeBaseMethod("spinElement_ValueChanging", sender, e);
    }

    protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
    {
        if (keyData == Keys.Tab)
        {
            (this.SpinElement as MySpinEditorElement).CommitText();
        }
       else if (keyData== Keys.Delete)
       {
           (this.SpinElement as MySpinEditorElement).NullableValue = null;
        } 
        return base.ProcessCmdKey(ref msg, keyData);
    }

    protected override Size DefaultSize
    {
        get
        {
            return GetDpiScaledSize(new Size(100, 20));
        }
    }
}

public class MySpinEditorElement : RadSpinElement
{
    private bool validating;
    private decimal? nullableValue;
    private RadButtonElement nullButton;

    public decimal? NullableValue
    {
        get
        {
            return this.nullableValue;
        }
        set
        {
            this.nullableValue = value;
            if (value.HasValue)
            {
                this.internalValue = value.Value;
            }
            else
            {
                this.internalValue = 0m;
            }

            this.Validate();
            this.OnNullableValueChanged();
        }
    }

    protected override void OnKeyDown(KeyEventArgs e)
    {
        if (e.KeyCode == Keys.Enter)
        {
            this.CommitText();
            e.Handled = true;
            return;
        }

        base.OnKeyDown(e);
    }

    void nullButton_Click(object sender, EventArgs e)
    {
        this.NullableValue = null;
    }

    public virtual void CommitText()
    {
        this.NullableValue = this.GetValueFromText();
    }

    protected override decimal GetValueFromText()
    {
        if (this.TextBoxItem.Text == "")
        {
            return 0m;
        }

        return base.GetValueFromText();
    }

    public override bool Validate()
    {
        if (!this.NullableValue.HasValue)
        {
            this.TextBoxItem.Text = "";
            return true;
        }

        this.TextBoxItem.Text = this.GetTextFromNumber(this.NullableValue.HasValue ? this.internalValue : 0m, this.Hexadecimal,
            this.ThousandsSeparator, this.DecimalPlaces);

        return true;
    }

    private string GetTextFromNumber(decimal num, bool hex, bool thousands, int decimalPlaces)
    {
        if (hex)
        {
            return string.Format("{0:X}", (long)num);
        }

        return num.ToString((thousands ? "N" : "F") + decimalPlaces.ToString(CultureInfo.CurrentCulture), CultureInfo.CurrentCulture);
    }

    public override void PerformStep(decimal step)
    {
        decimal value = this.GetValueFromText();

        try
        {
            decimal incValue = value + step;
            value = incValue;
        }
        catch (OverflowException)
        {
        }

        this.NullableValue = this.Constrain(value);
        this.Validate();
    }

    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadSpinElement);
        }
    }

    public event EventHandler NullableValueChanged;

    protected virtual void OnNullableValueChanged()
    {
        if (this.NullableValueChanged != null)
        {
            this.NullableValueChanged(this, EventArgs.Empty);
        }
    }
}