Why there is a possible null reference warning

// JetBrains ReSharper 8.2.1
// Build 8.2.1000.4556 on 2014-05-19T09:12:38

    public class Transformer
    {
        private void TransformElementBad(XElement field)
        {
            var format = string.Empty;

            if (field.Element("ViewFormatInfo") != null)
                format = field.Element("ViewFormatInfo").Value.Trim();

            Console.WriteLine(format);
        }

        private void TransformElementGood(XElement field)
        {
            var format = string.Empty;

            var element = field.Element("ViewFormatInfo");
            if (element != null)
                format = element.Value.Trim();

            Console.WriteLine(format);
        }
    }