Insert NULL into SQL when string is empty

Setting an empty string to null on Insert into database

/// <summary>
/// Databases the null if null.
/// </summary>
/// <param name="obj">The object.</param>
/// <returns>returns object</returns>
public static object DBNullIfNull(object obj)
{
    return obj != null ? obj : DBNull.Value;
}

/// <summary>
/// Databases the null if null or empty.
/// </summary>
/// <param name="str">The string.</param>
/// <returns>returns object</returns>
public static object DBNullIfNullOrEmpty(string str)
{
    return !String.IsNullOrEmpty(str) ? str : (object)DBNull.Value;
}