diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index ad24c08a78..a3959633c8 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -1,5 +1,3 @@
-// For format details, see https://aka.ms/devcontainer.json. For config options, see the
-// README at: https://github.com/devcontainers/templates/tree/main/src/javascript-node
 {
     "name": "NodeBB",
     "build": {
diff --git a/src/posts/category.js b/src/posts/category.js
index b87342a89f..aba16d1854 100644
--- a/src/posts/category.js
+++ b/src/posts/category.js
@@ -1,7 +1,5 @@
-
 'use strict';
 
-
 const _ = require('lodash');
 
 const db = require('../database');
@@ -11,36 +9,39 @@ const activitypub = require('../activitypub');
 module.exports = function (Posts) {
 	Posts.getCidByPid = async function (pid) {
 		const tid = await Posts.getPostField(pid, 'tid');
+
 		if (!tid && activitypub.helpers.isUri(pid)) {
 			return -1; // fediverse pseudo-category
 		}
-
-		return await topics.getTopicField(tid, 'cid');
+		return topics.getTopicField(tid, 'cid');
 	};
 
 	Posts.getCidsByPids = async function (pids) {
 		const postData = await Posts.getPostsFields(pids, ['tid']);
-		const tids = _.uniq(postData.map(post => post && post.tid).filter(Boolean));
+		const tids = _.uniq(postData.map(p => p && p.tid).filter(Boolean));
 		const topicData = await topics.getTopicsFields(tids, ['cid']);
 		const tidToTopic = _.zipObject(tids, topicData);
-		const cids = postData.map(post => tidToTopic[post.tid] && tidToTopic[post.tid].cid);
-		return cids;
+
+		// guard against null posts
+		return postData.map(p => (p && tidToTopic[p.tid] && tidToTopic[p.tid].cid) || undefined);
 	};
 
 	Posts.filterPidsByCid = async function (pids, cid) {
-		if (!cid) {
-			return pids;
-		}
+
+		if (!cid) return pids;
 
 		if (!Array.isArray(cid) || cid.length === 1) {
-			return await filterPidsBySingleCid(pids, cid);
+			return filterPidsBySingleCid(pids, cid);
 		}
+
 		const pidsArr = await Promise.all(cid.map(c => Posts.filterPidsByCid(pids, c)));
 		return _.union(...pidsArr);
 	};
 
 	async function filterPidsBySingleCid(pids, cid) {
-		const isMembers = await db.isSortedSetMembers(`cid:${parseInt(cid, 10)}:pids`, pids);
+		const cidNum = parseInt(Array.isArray(cid) ? cid[0] : cid, 10);
+		const key = `cid:${cidNum}:pids`;
+		const isMembers = await db.isSortedSetMembers(key, pids);
 		return pids.filter((pid, index) => pid && isMembers[index]);
 	}
-};
+};
\ No newline at end of file