Map nullable struct query results

Dapper/SqlMapper.cs

@@ -1964,6 +1964,11 @@ private static Func<DbDataReader, object> GetDeserializer(Type type, DbDataReade
             {
                 return GetDapperRowDeserializer(reader, startBound, length, returnNullIfFirstMissing);
             }
+
+            if (type.IsValueType && Nullable.GetUnderlyingType(type) is Type nullableType && !nullableType.IsEnum)
+            {
+                return GetDeserializer(nullableType, reader, startBound, length, returnNullIfFirstMissing);
+            }
 
             Type? underlyingType = null;
             bool useGetFieldValue = false;

Directory.Packages.props

@@ -38,6 +38,7 @@
     <PackageVersion Include="RepoDb.SqlServer" Version="1.13.1" />
     <PackageVersion Include="ServiceStack.OrmLite.SqlServer" Version="10.0.6" />
     <PackageVersion Include="Snowflake.Data" Version="5.5.0" />
+    <PackageVersion Include="pengdows.crud.fakeDb" Version="2.0.5" />
     <PackageVersion Include="SqlMarshal" Version="0.5.0" />
     <PackageVersion Include="SubSonic" Version="3.0.0.4" />
     <PackageVersion Include="Susanoo.SqlServer" Version="1.2.4.2" />

tests/Dapper.Tests/Dapper.Tests.csproj

@@ -32,6 +32,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' != 'net481'">
+    <PackageReference Include="pengdows.crud.fakeDb" />
     <PackageReference Include="Npgsql" />
     <PackageReference Include="Snowflake.Data" />
   </ItemGroup>

tests/Dapper.Tests/FakeDbTests.Issue1900.cs

@@ -0,0 +1,33 @@
+#if !NET481
+using System.Collections.Generic;
+using pengdows.crud.fakeDb;
+using Xunit;
+
+namespace Dapper.Tests;
+
+public sealed class FakeDbIssue1900Tests
+{
+    [Fact]
+    public void QuerySingleNullableStructMapsTheRow()
+    {
+        using var connection = new fakeDbConnection(new FakeDataStore());
+        connection.EnqueueReaderResult(new[]
+        {
+            new Dictionary<string, object?> { ["ID"] = 1, ["Name"] = "Something" },
+        });
+        connection.Open();
+
+        var result = connection.QuerySingle<Foo?>("select ID, Name");
+
+        Assert.True(result.HasValue);
+        Assert.Equal(1, result.Value.ID);
+        Assert.Equal("Something", result.Value.Name);
+    }
+
+    private struct Foo
+    {
+        public int ID { get; set; }
+        public string? Name { get; set; }
+    }
+}
+#endif