Change storage of BTRP_DUMMY.

include/buffer.h

@@ -228,8 +228,9 @@ LSUP_btriple_free (LSUP_BufferTriple *sspo);
 
 /** @brief Free a buffer triple and its buffer handles but not the buffer data.
  *
- * This is useful when freeing a "dummy" triple whose buffers are owned by the
- * caller but the data the terms point to are owned by the store.
+ * This is useful when freeing a dummy triple (#LSUP_BTRP_DUMMY) or a triple
+ * whose buffers are owned by the caller but the data the terms point to are
+ * owned by the store.
  *
  */
 void
@@ -279,6 +280,13 @@ LSUP_btriple_hash (const LSUP_BufferTriple *strp)
 }
 
 
-#define BTRP_DUMMY LSUP_btriple_new (NULL, NULL, NULL)
+/** @brief Dummy buffer triple.
+ *
+ * Triple of dummy buffer, with #LSUP_Buffer size space allocated, but no
+ * contents.
+ *
+ * Free with #LSUP_btriple_free_shallow().
+ */
+#define BTRP_DUMMY LSUP_btriple_new (BUF_DUMMY, BUF_DUMMY, BUF_DUMMY)
 
 #endif