feat: add IsNull to bindable property

src/BB84.Notifications/BindableProperty.cs

@@ -20,6 +20,9 @@ public sealed class BindableProperty<T> : IBindableProperty<T>
   public BindableProperty(T value)
     => _value = value;
 
+  /// <inheritdoc/>
+  public bool IsNull => _value is null;
+
   /// <inheritdoc/>
   public T Value
   {

src/BB84.Notifications/Interfaces/IBindableProperty.cs

@@ -8,6 +8,11 @@ namespace BB84.Notifications.Interfaces;
 /// <typeparam name="T">The value type to work with.</typeparam>
 public interface IBindableProperty<T> : INotifyPropertyChanged, INotifyPropertyChanging
 {
+  /// <summary>
+  /// Is the value of the bindable property null?
+  /// </summary>
+  bool IsNull { get; }
+
   /// <summary>
   /// The actual value of the bindable property.
   /// </summary>

tests/BB84.NotificationsTests/BindablePropertyTests.IsNull.cs

@@ -0,0 +1,23 @@
+using BB84.Notifications;
+using BB84.Notifications.Interfaces;
+
+namespace BB84.NotificationsTests;
+
+public sealed partial class BindablePropertyTests
+{
+  [DataTestMethod]
+  [DataRow(456, false)]
+  [DataRow(6.3d, false)]
+  [DataRow(0.75f, false)]
+  [DataRow(45623415L, false)]
+  [DataRow(0xFE, false)]
+  [DataRow(true, false)]
+  [DataRow("Test", false)]
+  [DataRow(null, true)]
+  public void IsNull(object? value, bool expected)
+  {
+    IBindableProperty<object?> bindableProperty = new BindableProperty<object?>(value);
+
+    Assert.AreEqual(expected, bindableProperty.IsNull);
+  }
+}