.InField with string argument

Hi!

I'm trying to use method InField with a string argument, but it doesn't seem to work.

            return client.Search<ProductPage>()
                .For(searchQuery)
                .InField(i => i.FullName)
                .GetPagesResult(); // returns results
            return client.Search<ProductPage>()
                .For(searchQuery)
                .InField("FullName")
                .GetPagesResult(); // doesn't return any result

What can be the problem?