diff --git a/R/file_utils.R b/R/file_utils.R
index 6e425dbc..8b2fd5b5 100644
--- a/R/file_utils.R
+++ b/R/file_utils.R
@@ -1163,6 +1163,7 @@ batch_load_twas_weights <- function(twas_weights_results, meta_data_df, max_memo
   )
 
   # Merge with meta_data_df to get TSS information
+  meta_data_df <- meta_data_df[!duplicated(meta_data_df[, c("region_id", "TSS")]), ]
   gene_memory_df <- merge(gene_memory_df, meta_data_df[, c("region_id", "TSS")],
     by.x = "gene_name",
     by.y = "region_id", all.x = TRUE
diff --git a/R/twas.R b/R/twas.R
index a70a51ef..ca4d8a07 100644
--- a/R/twas.R
+++ b/R/twas.R
@@ -576,7 +576,7 @@ twas_pipeline <- function(twas_weights_data,
     }
   }
   if (length(twas_weights_data)==0) {
-    return(NULL)
+    return(list(NULL))
   }
 
   # harmonize twas weights and gwas sumstats against LD
@@ -686,7 +686,7 @@ twas_pipeline <- function(twas_weights_data,
   gc()
   twas_results_db <- twas_results_db[!sapply(twas_results_db, function(x) is.null(x) || (is.list(x) && all(sapply(x, is.null))))]
   if (length(twas_results_db) == 0) {
-    return(NULL)
+    return(list(NULL))
   }
   twas_results_table <- do.call(rbind, lapply(twas_results_db, function(x) x$twas_table))
   mr_results <- do.call(rbind, lapply(twas_results_db, function(x) x$mr_result))