Fix TryGetMappedNullability for CompositeCustomType

Fixes #2937

Author: PleasantD

src/NHibernate.Test/Linq/TryGetMappedTests.cs

@@ -272,6 +272,18 @@ public void NestedComponentPropertyCastTest()
 				o => o?.Name == "component[OtherProperty1]");
 		}
 
+		[Test]
+		public void CompositePropertyTest()
+		{
+			var query = session.Query<Glarch>().Select(o => o.Multiple.count);
+			AssertSupported(
+				query,
+				typeof(Glarch).FullName,
+				"Multiple.count",
+				o => o is Int32Type,
+				o => o?.Name == typeof(MultiplicityType).FullName);
+		}
+
 		[Test]
 		public void ManyToOneTest()
 		{

src/NHibernate/Util/ExpressionsHelper.cs

@@ -158,7 +158,11 @@ internal static bool TryGetMappedNullability(
 			}
 
 			int index;
-			if (componentType != null)
+			if (componentType is CompositeCustomType cct)
+			{
+				memberPath = memberPath.Remove(memberPath.LastIndexOf('.'));
+			}
+			else if (componentType != null)
 			{
 				index = Array.IndexOf(
 					componentType.PropertyNames,