Fixes

Author: bahusoid

src/NHibernate/Hql/Ast/ANTLR/Tree/CaseNode.cs

@@ -29,17 +29,38 @@ public override IType  DataType
 				if (ExpectedType != null)
 					return ExpectedType;
 
-				foreach (var node in GetResultNodes())
+				if (base.DataType != null)
+					return base.DataType;
+
+				var dataType = GetTypeFromResultNodes();
+
+				foreach (var node in GetResultNodes().OfType<ISelectExpression>())
 				{
-					if (node is ISelectExpression select && !(node is ParameterNode))
-						return select.DataType;
+					if (node.DataType == null && node is IExpectedTypeAwareNode typeAwareNode)
+					{
+						typeAwareNode.ExpectedType = dataType;
+					}
 				}
 
-				throw new HibernateException("Unable to determine data type of CASE statement.");
+				base.DataType = dataType;
+				return dataType;
 			}
 			set { base.DataType = value; }
 		}
 
+		private IType GetTypeFromResultNodes()
+		{
+			foreach (var node in GetResultNodes())
+			{
+				if (node is ISelectExpression select && select.DataType != null)
+				{
+					return select.DataType;
+				}
+			}
+
+			throw new HibernateException("Unable to determine data type of CASE statement.");
+		}
+
 		public IEnumerable<IASTNode> GetResultNodes()
 		{
 			for (int i = 0; i < ChildCount; i++)

src/NHibernate/Linq/Functions/StringGenerator.cs

@@ -217,7 +217,8 @@ public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject,
 		{
 			var expression = visitor.Visit(targetObject).AsExpression();
 			var index = treeBuilder.Add(visitor.Visit(arguments[0]).AsExpression(), treeBuilder.Constant(1));
-			return treeBuilder.MethodCall("substring", expression, index, treeBuilder.Constant(1));
+
+			return treeBuilder.TransparentCast(treeBuilder.MethodCall("substring", expression, index, treeBuilder.Constant(1)), typeof(char));
 		}
 	}