diff --git a/src/bmsparsevec_compr.h b/src/bmsparsevec_compr.h
index ed774c6d..5dbaf09f 100644
--- a/src/bmsparsevec_compr.h
+++ b/src/bmsparsevec_compr.h
@@ -280,7 +280,10 @@ public:
         
         /** add a series of consequitve NULLs (no-value) to the container */
         void add_null(size_type count) BMNOEXCEPT;
-        
+
+        /** return true if insertion buffer is empty */
+        bool empty() const { return sv_bi_.empty(); }
+
         /** flush the accumulated buffer */
         void flush();
     protected: