Dapper: custom type handler for struct

My aim is to create custom struct that wrapping double and save it to database using Dapper. Unfortunately I've faced a problem I can't fix.

I've created following struct:

public struct MyDouble
{
        private readonly double value;
        public static implicit operator MyDouble(double val)
        {
            return new MyDouble(val);
        }

        public static explicit operator double(MyDouble val)
        {
            return val.value;
        }

        public static explicit operator MyDouble(int val)
        {
            return new MyDouble(val);
        }

        public MyDouble(double val)
        {
            this.value = Process(val);
        }

        public double GetDouble()
        {
            return this.value;
        }
}

and added custom type handler as it described here (https://medium.com/dapper-net/custom-type-handling-4b447b97c620)

public class MyDoubleTypeHandler : SqlMapper.TypeHandler<MyDouble>
{
    public override MyDouble Parse(object value)
    {
        return (MyDouble)value;
    }

    public override void SetValue(IDbDataParameter parameter, MyDouble value)
    {
        parameter.DbType = DbType.Double;
        parameter.Value = value.GetDouble();
    }
}

My custom objects with MyDouble prop inside:

public class MyObject
{
    public MyDouble Prop1 { get; set; }
}

And save method looks like:

public async Task<bool> Save(List<MyObject> data)
{
    SqlMapper.ResetTypeHandlers();
    SqlMapper.AddTypeHandler(new MyDoubleTypeHandler());
    parameters.AddTable("@Data", "dbo.MyObject", data.AsList());

    using (var connection = new SqlConnection(connectionString))
    {
        await connection.OpenAsync();
        return await connection.ExecuteAsync("name-of-sp", parameters, commandType: CommandType.StoredProcedure);
    }
}

As a result I get this error: "System.ArgumentException: The type of column 'Prop1' is not supported. The type is 'MyDouble'".

It seems to be that my custom type handler hasn't been registered despite the fact I do it directly by calling SqlMapper.AddTypeHandler(new MyDoubleTypeHandler());

Could anyone help with that problem?

P.S. I'm using Dapper 1.50.5, Dapper.ParameterExtensions 2018.12.7.1 inside Asp.NET Core app (2.1)