Small doc improvement.
diff --git a/include/freetype/freetype.h b/include/freetype/freetype.h
index 8fc477d..0a013e8 100644
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -799,6 +799,8 @@ FT_BEGIN_HEADER
/* provide localized and Unicode versions of */
/* this string. Applications should use the */
/* format specific interface to access them. */
+ /* Can be NULL (e.g., in fonts embedded in a */
+ /* PDF file). */
/* */
/* style_name :: The face's style name. This is an ASCII */
/* string, usually in English, which describes */