diff --git a/src/wireviz/wv_bom.py b/src/wireviz/wv_bom.py
index 0328661..223de38 100644
--- a/src/wireviz/wv_bom.py
+++ b/src/wireviz/wv_bom.py
@@ -3,7 +3,7 @@
 
 from collections import Counter
 from dataclasses import asdict
-from typing import List, Tuple, Union
+from typing import Any, List, Tuple, Union
 
 from wireviz.DataClasses import AdditionalComponent, Connector, Cable
 from wireviz.wv_gv_html import html_line_breaks
@@ -106,8 +106,7 @@ def generate_bom(harness):
         group_entries = [v for v in bom_entries if bom_types_group(v) == group]
         designators = []
         for group_entry in group_entries:
-            d = group_entry.get('designators')
-            designators.extend(d if isinstance(d, List) else [d] if d else [])
+            designators.extend(make_list(group_entry.get('designators')))
         total_qty = sum(entry['qty'] for entry in group_entries)
         bom.append({**group_entries[0], 'qty': round(total_qty, 3), 'designators': sorted(set(designators))})
 
@@ -129,19 +128,13 @@ def bom_list(bom):
     for fieldname in ['pn', 'manufacturer', 'mpn']: # these optional BOM columns will only be included if at least one BOM item actually uses them
         if any(entry.get(fieldname) for entry in bom):
             keys.append(fieldname)
-    bom_list = []
     # list of staic bom header names,  headers not specified here are generated by capitilising the internal name
     bom_headings = {
         "pn": "P/N",
         "mpn": "MPN"
     }
-    bom_list.append([bom_headings.get(k, k.capitalize()) for k in keys])  # create header row with keys
-    for item in bom:
-        item_list = [item.get(key, '') for key in keys]  # fill missing values with blanks
-        item_list = [', '.join(subitem) if isinstance(subitem, List) else subitem for subitem in item_list]  # convert any lists into comma separated strings
-        item_list = ['' if subitem is None else subitem for subitem in item_list]  # if a field is missing for some (but not all) BOM items
-        bom_list.append(item_list)
-    return bom_list
+    return ([[bom_headings.get(k, k.capitalize()) for k in keys]] +  # Create header row with key names
+            [[make_str(entry.get(k)) for k in keys] for entry in bom])  # Create string list for each entry row
 
 def component_table_entry(type, qty, unit=None, pn=None, manufacturer=None, mpn=None):
     output = f'{qty}'
@@ -174,3 +167,11 @@ def manufacturer_info_field(manufacturer, mpn):
 # Return the value indexed if it is a list, or simply the value otherwise.
 def index_if_list(value, index):
     return value[index] if isinstance(value, list) else value
+
+def make_list(value: Any) -> list:
+    """Return value if a list, empty list if None, or single element list otherwise."""
+    return value if isinstance(value, list) else [] if value is None else [value]
+
+def make_str(value: Any) -> str:
+    """Return comma separated elements if a list, empty string if None, or value as a string otherwise."""
+    return ', '.join(str(element) for element in make_list(value))