Treat falsy values as valid for i18n placeholders & fix groups in common message

_locales/en/messages.json

@@ -4430,8 +4430,16 @@
   },
   "ConversationDetailsGroups--title": {
     "message": "$number$ groups in common",
+    "description": "(deleted 2023/01/03) Title of the groups-in-common panel, in the contact details"
+  },
+  "icu:ConversationDetailsGroups--title": {
+    "messageformat": "{count, plural, one {1 group} other {# groups}} in common",
     "description": "Title of the groups-in-common panel, in the contact details"
   },
+  "icu:ConversationDetailsGroups--title--with-zero-groups-in-common": {
+    "messageformat": "No groups in common",
+    "description": "Title of the groups-in-common panel, in the contact details, with zero groups in common"
+  },
   "ConversationDetailsGroups--add-to-group": {
     "message": "Add to a group",
     "description": "The button shown on a conversation details (for a direct contact) that you can click to add that contact to groups"

ts/components/conversation/conversation-details/ConversationDetailsGroups.tsx

@@ -37,9 +37,15 @@ export function ConversationDetailsGroups({
 
   return (
     <PanelSection
-      title={i18n('ConversationDetailsGroups--title', {
-        number: groupsInCommon.length,
-      })}
+      title={
+        groupsInCommon.length > 0
+          ? i18n('icu:ConversationDetailsGroups--title', {
+              count: groupsInCommon.length,
+            })
+          : i18n(
+              'icu:ConversationDetailsGroups--title--with-zero-groups-in-common'
+            )
+      }
     >
       <PanelRow
         icon={<div className="ConversationDetails-groups__add-to-group-icon" />}

ts/util/setupI18n.ts

@@ -145,13 +145,14 @@ export function setupI18n(
       }
 
       const placeholderName = match[1];
-      const value = substitutions[placeholderName];
-      if (!value) {
+      let value = substitutions[placeholderName];
+      if (value == null) {
         log.error(
           `i18n: Value not provided for placeholder ${placeholderName} in key '${key}'`
         );
+        value = '';
       }
-      builder += value || '';
+      builder += value;
 
       lastTextIndex = FIND_REPLACEMENTS.lastIndex;
       match = FIND_REPLACEMENTS.exec(message);