System.Data.DefaultValueTypeConverter.ConvertFrom C# (CSharp) Метод

        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
        {
            if (value != null && value.GetType() == typeof(string))
            {
                string strValue = (string)value;
                if (string.Equals(strValue, NullString, StringComparison.OrdinalIgnoreCase))
                {
                    return null;
                }
                else if (string.Equals(strValue, DbNullString, StringComparison.OrdinalIgnoreCase))
                {
                    return DBNull.Value;
                }
            }

            return base.ConvertFrom(context, culture, value);
        }
    }