Allow usage of private setter

src/FubarDev.BeanIO/Internal/Util/BeanUtil.cs

@@ -354,7 +354,7 @@ private string RemovePrefixForSetter(string setterName)
                 var typeInfo = _typeInfo;
                 while (typeInfo != typeof(object))
                 {
-                    methodInfo = typeInfo.GetMethod(name);
+                    methodInfo = typeInfo.GetMethod(name, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
                     if (methodInfo != null)
                         break;
                     if (typeInfo.BaseType == null)

test/FubarDev.BeanIO.Test/Beans/Bean.cs

@@ -37,5 +37,14 @@ public class Bean
         public Bean? record;
         public Bean? segment;
         #endregion
+
+        public int? NoOpSetter
+        {
+            get => 1;
+        }
+
+        private void SetNoOpSetter(int? value)
+        {
+        }
     }
 }

test/FubarDev.BeanIO.Test/Issues/PrivateSetterTests.cs

@@ -0,0 +1,32 @@
+// <copyright file="PrivateSetterTests.cs" company="Fubar Development Junker">
+// Copyright (c) 2016 Fubar Development Junker. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+// </copyright>
+
+using BeanIO.Beans;
+using BeanIO.Builder;
+
+using Xunit;
+
+namespace BeanIO.Issues;
+
+public class PrivateSetterTests
+{
+    [Fact]
+    public void TestPrivateSetter()
+    {
+        var factory = StreamFactory.NewInstance();
+        factory.Define(
+            new StreamBuilder("s")
+                .Format("fixedlength")
+                .AddRecord(
+                    new RecordBuilder("r", typeof(Bean))
+                        .AddField(new FieldBuilder(nameof(Bean.NoOpSetter))
+                            .Length(1)
+                            .RegEx("[0-9]")
+                            .Setter("SetNoOpSetter"))));
+        var unmarshaller = factory.CreateUnmarshaller("s");
+        var bean = Assert.IsType<Bean>(unmarshaller.Unmarshal("1"));
+        Assert.Equal(1, bean.NoOpSetter);
+    }
+}