@@ -221,7 +221,11 @@ BSmooth <- function(BSseq,

     # Set up "parallel" ArrayGrid over pos

     pos_grid <- ArbitraryArrayGrid(list(row_tickmarks, 1L))

     # Construct RealizationSink objects (as required)

-    if (BACKEND == "HDF5Array") {

+    if (is.null(BACKEND)) {

+        coef_sink <- NULL

+        se.coef_sink <- NULL

+        sink_lock <- NULL

+    } else if (BACKEND == "HDF5Array") {

         coef_sink <- HDF5RealizationSink(

             dim = dim(M),

             # NOTE: Never allow dimnames.