diff --git a/R/AddStep.R b/R/AddStep.R
index f797e5704205b5cf01a1230dca077dd7e0700106..fece57225aec829518468ceb4911c4e90d5299f5 100644
--- a/R/AddStep.R
+++ b/R/AddStep.R
@@ -70,8 +70,12 @@ AddStep <- function(inputs, step_fun, ...) {
     workflow <- list(inputs = inputs,
                      fun = step_fun,
                      params = list(...))
-    dimensions <- rep(NA, length(attr(step_fun, 'OutputDims')[[output]]))
-    names(dimensions) <- attr(step_fun, 'OutputDims')[[output]]
+    if (!is.null(attr(step_fun, 'OutputDims')[[output]])) {
+      dimensions <- rep(NA, length(attr(step_fun, 'OutputDims')[[output]]))
+      names(dimensions) <- attr(step_fun, 'OutputDims')[[output]]
+    } else {
+      dimensions <- NULL
+    }
     in_dims_to_remove <- which(names(all_input_dims) %in% new_target_dims)
     if (length(in_dims_to_remove) > 0) {
       dimensions <- c(dimensions, all_input_dims[-in_dims_to_remove])
diff --git a/R/ByChunks.R b/R/ByChunks.R
index 6e7d64c91093bb3f5b20ac037ce0f041134543f2..a0c6c4a720ea96cdbffbe2addf5f958df3c6da98 100644
--- a/R/ByChunks.R
+++ b/R/ByChunks.R
@@ -121,7 +121,7 @@ ByChunks <- function(step_fun, cube_headers, ..., chunks = 'auto',
   # Check all input headers have matching dimensions
   cube_index <- 1
   for (cube_header in cube_headers) {
-    if (!all(attr(cube_header, 'Dimensions') == unlist(all_dims)[names(attr(cube_header, 'Dimensions'))])) {
+    if (!all(attr(cube_header, 'Dimensions') == all_dims_merged[names(attr(cube_header, 'Dimensions'))])) {
       stop("All provided 'cube_headers' must have matching dimension lengths ",
            "with each other.")
     }
@@ -158,9 +158,9 @@ ByChunks <- function(step_fun, cube_headers, ..., chunks = 'auto',
     stop("All values in parameter 'chunks' must be >= 1.")
   }
   for (chunk_spec in 1:length(chunks)) {
-    if (chunks[[chunk_spec]] > unlist(all_dims)[names(chunks)[chunk_spec]]) {
+    if (chunks[[chunk_spec]] > all_dims_merged[names(chunks)[chunk_spec]]) {
       stop("Too many chunks requested for the dimension ", names(chunks)[chunk_spec], 
-           ". Maximum allowed is ", unlist(all_dims)[names(chunks)[chunk_spec]])
+           ". Maximum allowed is ", all_dims_merged[names(chunks)[chunk_spec]])
     }
   }
   default_chunks[names(chunks)] <- chunks
diff --git a/R/Compute.R b/R/Compute.R
index f08cb03bec26e6ce484e20e29384f9a88aafb640..5dd0c5cefff37c4242eb00747ac397c979a4e7be 100644
--- a/R/Compute.R
+++ b/R/Compute.R
@@ -39,8 +39,8 @@ Compute <- function(workflow, chunks = 'auto',
                       paste(paste0('input', 1:length(workflow$inputs)),
                             collapse = ", "))
     if (length(workflow$params) > 0) {
-      op_text <- paste0(op_text, ", ")
       for (j in 1:length(workflow$params)) {
+        op_text <- paste0(op_text, ", ")
         op_text <- paste0(op_text, names(workflow$params)[j], " = ",
                           paste(deparse(workflow$params[[j]]), collapse = '\n'))
       }
diff --git a/R/Step.R b/R/Step.R
index f215d9bac252802c40c5b4a9b458250059a28e93..d08595ab4adcb46105de7f381b31716b3bca8aa2 100644
--- a/R/Step.R
+++ b/R/Step.R
@@ -24,14 +24,14 @@ Step <- function(fun, target_dims, output_dims) {
   }
 
   # Check output_dims
-  if (is.character(output_dims)) {
+  if (is.character(output_dims) || is.null(output_dims)) {
     output_dims <- list(output_dims)
     names(output_dims) <- 'output1'
   }
   if (is.list(output_dims)) {
     sapply(output_dims, 
       function(x) {
-        if (!(is.character(x) && (length(x) > 0))) {
+        if (!(is.character(x) || is.null(x))) {
           stop("Parameter 'output_dims' must be one or a list of vectors ",
                "of target dimension names for each data array input in ",
                "the function 'fun'.")