Small class for making SQL calls to SQL Server from .NET Core

Database.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;

namespace Core.Data
{
    /// <summary>
    /// 
    /// </summary>
    public class Database
    {
        private readonly String _connectionString;

        public Database(string connectionString)
        {
            _connectionString = connectionString;
        }

        public Object ExecuteScalar(string sql, Dictionary<String, Object> parameters = null)
        {
            using (var connection = new SqlConnection(_connectionString))
            {
                var command = CreateCommand(connection, sql, parameters);

                connection.Open();
                var result = command.ExecuteScalar();
                connection.Close();

                return result;
            }
        }

        public void ExecuteNonQuery(string sql, Dictionary<String, Object> parameters = null)
        {
            using (var connection = new SqlConnection(_connectionString))
            {
                var command = CreateCommand(connection, sql, parameters);

                connection.Open();
                command.ExecuteNonQuery();
                connection.Close();
            }
        }

        public IEnumerable<T> Execute<T>(string sql, Func<IDataReader, T> map, Dictionary<String, Object> parameters = null)
        {
            var result = new List<T>();

            using (var connection = new SqlConnection(_connectionString))
            {
                var command = CreateCommand(connection, sql, parameters);

                connection.Open();

                using (var reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        if (map != null)
                        {
                            result.Add(map(reader));
                        }
                    }
                }

                connection.Close();
            }

            return result;
        }

        private SqlCommand CreateCommand(SqlConnection connection, String sql, Dictionary<String, Object> parameters = null)
        {
            var command = new SqlCommand(sql, connection);

            if (parameters != null)
            {
                foreach (var p in parameters)
                {
                    command.Parameters.Add(new SqlParameter
                    {
                        ParameterName = p.Key,
                        Value = p.Value
                    });
                }
            }

            return command;
        }
    }
}