capabilities: avoid NRE when ValueOrBinding<int>? is set to null

src/Framework/Framework/Binding/DotvvmCapabilityProperty.Helpers.cs

@@ -15,7 +15,14 @@ internal static class Helpers
             public static ValueOrBinding<T>? GetOptionalValueOrBinding<T>(DotvvmBindableObject c, DotvvmProperty p)
             {
                 if (c.properties.TryGet(p, out var x))
-                    return ValueOrBinding<T>.FromBoxedValue(x);
+                {
+                    // we want to return ValueOrBinding(null) -- "property set to null"
+                    // but if that isn't possible, it's better to return null ("property missing") than crash
+                    if (x is null && default(T) != null)
+                        return null;
+                    else
+                        return ValueOrBinding<T>.FromBoxedValue(x);
+                }
                 else return null;
             }
             public static ValueOrBinding<T> GetValueOrBinding<T>(DotvvmBindableObject c, DotvvmProperty p)
@@ -27,7 +34,15 @@ public static ValueOrBinding<T> GetValueOrBinding<T>(DotvvmBindableObject c, Dot
             public static ValueOrBinding<T>? GetOptionalValueOrBindingSlow<T>(DotvvmBindableObject c, DotvvmProperty p)
             {
                 if (c.IsPropertySet(p))
-                    return ValueOrBinding<T>.FromBoxedValue(c.GetValue(p));
+                {
+                    var x = c.GetValue(p);
+                    // we want to return ValueOrBinding(null) -- "property set to null"
+                    // but if that isn't possible, it's better to return null ("property missing") than crash
+                    if (x is null && default(T) != null)
+                        return null;
+                    else
+                        return ValueOrBinding<T>.FromBoxedValue(x);
+                }
                 else return null;
             }
             public static ValueOrBinding<T> GetValueOrBindingSlow<T>(DotvvmBindableObject c, DotvvmProperty p)

src/Framework/Framework/Controls/CompositeControl.cs

@@ -126,7 +126,8 @@ Func<IDotvvmRequestContext, CompositeControl, object> compileGetter(IControlAttr
         }
 
         static internal ControlInfo GetControlInfo(Type controlType) =>
-            controlInfoCache[controlType];
+            controlInfoCache.TryGetValue(controlType, out var result) ? result :
+                throw new Exception($"CompositeControl {controlType.FullName} wasn't initialized and GetContents cannot be executed. This is probably caused by a failure during property registration.");
 
         internal IEnumerable<DotvvmControl> ExecuteGetContents(IDotvvmRequestContext context)
         {

src/Tests/Runtime/CapabilityPropertyTests.cs

@@ -215,6 +215,33 @@ public void BitMoreComplexCapability_WeirdProperties_GetterAndSetter()
         }
 
 
+        [DataTestMethod]
+        [DataRow(typeof(TestControl6))]
+        [DataRow(typeof(TestControlFallbackProps))]
+        [DataRow(typeof(TestControlInheritedProps))]
+        public void BitMoreComplexCapability_NullableValue(Type controlType)
+        {
+            var control1 = (DotvvmBindableObject)Activator.CreateInstance(controlType);
+            var capProp = DotvvmCapabilityProperty.Find(controlType, typeof(BitMoreComplexCapability));
+
+            Assert.IsFalse(control1.GetCapability<BitMoreComplexCapability>().Nullable.HasValue);
+
+            control1.SetProperty("Nullable", null);
+            XAssert.Single(control1.Properties);
+            Assert.IsFalse(control1.GetCapability<BitMoreComplexCapability>().Nullable.HasValue);
+
+            control1.SetProperty("Nullable", 1);
+            Assert.AreEqual(1, control1.GetCapability<BitMoreComplexCapability>().Nullable);
+
+            control1.SetValue(capProp, new BitMoreComplexCapability { Nullable = null });
+            Assert.AreEqual(null, control1.GetCapability<BitMoreComplexCapability>().Nullable);
+            Assert.IsTrue(control1.IsPropertySet(control1.GetDotvvmProperty("Nullable")));
+
+            control1.SetValue(capProp, new BitMoreComplexCapability { Nullable = 2 });
+            Assert.AreEqual(2, control1.GetCapability<BitMoreComplexCapability>().Nullable);
+        }
+
+
         public class TestControl1:
             HtmlGenericControl,
             IObjectWithCapability<HtmlCapability>,
@@ -301,6 +328,7 @@ public int ValueOrBindingNullable2
             }
             public static readonly DotvvmProperty ValueOrBindingNullable2Property =
                 DotvvmProperty.Register<int, TestControlFallbackProps>(nameof(ValueOrBindingNullable2), defaultValue: 10);
+
             [PropertyAlias("ValueOrBindingNullable2")]
             public static readonly DotvvmProperty ValueOrBindingNullableProperty =
                 DotvvmPropertyAlias.RegisterAlias<TestControlFallbackProps>("ValueOrBindingNullable");
@@ -309,6 +337,30 @@ public int ValueOrBindingNullable2
                 DotvvmCapabilityProperty.RegisterCapability<BitMoreComplexCapability, TestControlFallbackProps>();
         }
 
+        public class TestControlInheritedProps:
+            HtmlGenericControl,
+            IObjectWithCapability<BitMoreComplexCapability>
+        {
+            public int NotNullable
+            {
+                get { return (int)GetValue(NotNullableProperty); }
+                set { SetValue(NotNullableProperty, value); }
+            }
+            public static readonly DotvvmProperty NotNullableProperty =
+                DotvvmProperty.Register<int, TestControlInheritedProps>(nameof(NotNullable), isValueInherited: true);
+
+            public int? Nullable
+            {
+                get { return (int?)GetValue(NullableProperty); }
+                set { SetValue(NullableProperty, value); }
+            }
+            public static readonly DotvvmProperty NullableProperty =
+                DotvvmProperty.Register<int?, TestControlInheritedProps>(nameof(Nullable), isValueInherited: true);
+
+            public static readonly DotvvmCapabilityProperty BitMoreComplexCapabilityProperty =
+                DotvvmCapabilityProperty.RegisterCapability<BitMoreComplexCapability, TestControlInheritedProps>();
+        }
+
         [DotvvmControlCapability]
         public sealed record TestCapability
         {