Fix net461 build

Author: bahusoid

src/NHibernate/Linq/Functions/StringGenerator.cs

@@ -260,21 +260,27 @@ public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject,
 
 	public class ReplaceGenerator : BaseHqlGeneratorForMethod
 	{
+#if NETCOREAPP2_0  
 		private static readonly MethodInfo MethodWithComparer = ReflectHelper.GetMethodDefinition<string>(x => x.Replace(string.Empty, string.Empty, default(StringComparison)));
+#endif
 
 		public ReplaceGenerator()
 		{
 			SupportedMethods = new[]
-									{
-										ReflectHelper.GetMethodDefinition<string>(s => s.Replace(' ', ' ')),
-										ReflectHelper.GetMethodDefinition<string>(s => s.Replace("", "")),
-										MethodWithComparer,
-									};
+			{
+				ReflectHelper.GetMethodDefinition<string>(s => s.Replace(' ', ' ')),
+				ReflectHelper.GetMethodDefinition<string>(s => s.Replace("", "")),
+#if NETCOREAPP2_0
+				MethodWithComparer,
+#endif
+			};
 		}
 
 		public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject, ReadOnlyCollection<Expression> arguments, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
 		{
+#if NETCOREAPP2_0
 			LogIgnoredStringComparisonParameter(method, MethodWithComparer);
+#endif
 			return treeBuilder.MethodCall(
 				"replace",
 				visitor.Visit(targetObject).AsExpression(),