Don't use NULL in public headers

src/hb-buffer.h

@@ -132,8 +132,8 @@ typedef struct hb_segment_properties_t {
 #define HB_SEGMENT_PROPERTIES_DEFAULT {HB_DIRECTION_INVALID, \
 				       HB_SCRIPT_INVALID, \
 				       HB_LANGUAGE_INVALID, \
-				       NULL, \
+				       (void *) 0, \
-				       NULL}
+				       (void *) 0}
 
 HB_EXTERN hb_bool_t
 hb_segment_properties_equal (const hb_segment_properties_t *a,

src/hb-common.h

@@ -134,7 +134,7 @@ hb_language_from_string (const char *str, int len);
 HB_EXTERN const char *
 hb_language_to_string (hb_language_t language);
 
-#define HB_LANGUAGE_INVALID ((hb_language_t) NULL)
+#define HB_LANGUAGE_INVALID ((hb_language_t) 0)
 
 HB_EXTERN hb_language_t
 hb_language_get_default (void);