[Semantics] Added test case for nullable constant value / fixed last

fix.

ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.TestCase.cs

@@ -327,4 +327,9 @@ namespace ICSharpCode.NRefactory.TypeSystem.TestCase
 			get { return 0; }
 		}
 	}
+
+	public class ClassWithMethodThatHasNullableDefaultParameter {
+		public void Foo (int? bar = 42) { }
+	}
+
 }

ICSharpCode.NRefactory.Tests/TypeSystem/TypeSystemTests.cs

@@ -1200,5 +1200,13 @@ namespace ICSharpCode.NRefactory.TypeSystem
 			var indexer = type.GetProperties(p => p.IsIndexer).Single();
 			Assert.AreEqual("Foo", indexer.Name);
 		}
+
+		[Test]
+		public void TestNullableDefaultParameter()
+		{
+			ITypeDefinition type = GetTypeDefinition(typeof(ClassWithMethodThatHasNullableDefaultParameter));
+			var method = type.GetMethods ().Single (m => m.Name == "Foo");
+			Assert.AreEqual(42, method.Parameters.Single ().ConstantValue);
+		}
 	}
 }

ICSharpCode.NRefactory/TypeSystem/Implementation/DefaultUnresolvedParameter.cs

@@ -235,17 +235,17 @@ namespace ICSharpCode.NRefactory.TypeSystem.Implementation
 			public object ConstantValue {
 				get {
 					ResolveResult rr = LazyInit.VolatileRead(ref this.resolvedDefaultValue);
+					if (rr == null) {
+						rr = defaultValue.Resolve(context);
+						LazyInit.GetOrSet(ref this.resolvedDefaultValue, rr);
+					}
 					if (rr is ConversionResolveResult) {
 						var crr = (ConversionResolveResult)rr;
 						if (crr.Conversion.IsNullableConversion)
 							return crr.Input.ConstantValue;
 					}
-					if (rr != null) {
+					return rr.ConstantValue;
-						return rr.ConstantValue;
+
-					} else {
-						rr = defaultValue.Resolve(context);
-						return LazyInit.GetOrSet(ref this.resolvedDefaultValue, rr).ConstantValue;
-					}
 				}
 			}