diff --git a/extensions/amazon-bedrock/discovery.ts b/extensions/amazon-bedrock/discovery.ts
index d04b709dad7..b7a9eaa756f 100644
--- a/extensions/amazon-bedrock/discovery.ts
+++ b/extensions/amazon-bedrock/discovery.ts
@@ -13,7 +13,10 @@ import type {
   ModelDefinitionConfig,
   ModelProviderConfig,
 } from "openclaw/plugin-sdk/provider-model-shared";
-import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "openclaw/plugin-sdk/text-runtime";
 
 const log = createSubsystemLogger("bedrock-discovery");
 
@@ -69,7 +72,7 @@ function buildCacheKey(params: {
 }
 
 function includesTextModalities(modalities?: Array<string>): boolean {
-  return (modalities ?? []).some((entry) => entry.toLowerCase() === "text");
+  return (modalities ?? []).some((entry) => normalizeOptionalLowercaseString(entry) === "text");
 }
 
 function isActive(summary: BedrockModelSummary): boolean {
@@ -81,7 +84,7 @@ function mapInputModalities(summary: BedrockModelSummary): Array<"text" | "image
   const inputs = summary.inputModalities ?? [];
   const mapped = new Set<"text" | "image">();
   for (const modality of inputs) {
-    const lower = modality.toLowerCase();
+    const lower = normalizeOptionalLowercaseString(modality);
     if (lower === "text") {
       mapped.add("text");
     }
@@ -96,7 +99,9 @@ function mapInputModalities(summary: BedrockModelSummary): Array<"text" | "image
 }
 
 function inferReasoningSupport(summary: BedrockModelSummary): boolean {
-  const haystack = `${summary.modelId ?? ""} ${summary.modelName ?? ""}`.toLowerCase();
+  const haystack = normalizeLowercaseStringOrEmpty(
+    `${summary.modelId ?? ""} ${summary.modelName ?? ""}`,
+  );
   return haystack.includes("reasoning") || haystack.includes("thinking");
 }
 
@@ -256,7 +261,9 @@ function resolveInferenceProfiles(
       const models = profile.models ?? [];
       const matchesFilter = models.some((m) => {
         const provider = m.modelArn?.split("/")?.[1]?.split(".")?.[0];
-        return provider ? providerFilter.includes(provider.toLowerCase()) : false;
+        return provider
+          ? providerFilter.includes(normalizeOptionalLowercaseString(provider) ?? "")
+          : false;
       });
       if (!matchesFilter) {
         continue;
@@ -265,7 +272,9 @@ function resolveInferenceProfiles(
 
     // Look up the underlying foundation model to inherit its capabilities.
     const baseModelId = resolveBaseModelId(profile);
-    const baseModel = baseModelId ? foundationModels.get(baseModelId.toLowerCase()) : undefined;
+    const baseModel = baseModelId
+      ? foundationModels.get(normalizeLowercaseStringOrEmpty(baseModelId))
+      : undefined;
 
     discovered.push({
       id: profile.inferenceProfileId,
@@ -356,8 +365,9 @@ export async function discoverBedrockModels(params: {
         maxTokens: defaultMaxTokens,
       });
       discovered.push(def);
-      seenIds.add(def.id.toLowerCase());
-      foundationModels.set(def.id.toLowerCase(), def);
+      const normalizedId = normalizeLowercaseStringOrEmpty(def.id);
+      seenIds.add(normalizedId);
+      foundationModels.set(normalizedId, def);
     }
 
     // Merge inference profiles — inherit capabilities from foundation models.
@@ -368,9 +378,10 @@ export async function discoverBedrockModels(params: {
       foundationModels,
     );
     for (const profile of inferenceProfiles) {
-      if (!seenIds.has(profile.id.toLowerCase())) {
+      const normalizedId = normalizeLowercaseStringOrEmpty(profile.id);
+      if (!seenIds.has(normalizedId)) {
         discovered.push(profile);
-        seenIds.add(profile.id.toLowerCase());
+        seenIds.add(normalizedId);
       }
     }
 
diff --git a/extensions/line/src/card-command.ts b/extensions/line/src/card-command.ts
index 1fb02e8adb9..2f3574470ff 100644
--- a/extensions/line/src/card-command.ts
+++ b/extensions/line/src/card-command.ts
@@ -1,5 +1,6 @@
 import type { OpenClawPluginApi } from "openclaw/plugin-sdk/core";
 import type { ReplyPayload } from "openclaw/plugin-sdk/reply-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import {
   createActionCard,
   createImageCard,
@@ -136,7 +137,7 @@ function parseCardArgs(argsStr: string): {
   // Extract type (first word)
   const typeMatch = argsStr.match(/^(\w+)/);
   if (typeMatch) {
-    result.type = typeMatch[1].toLowerCase();
+    result.type = normalizeLowercaseStringOrEmpty(typeMatch[1]);
     argsStr = argsStr.slice(typeMatch[0].length).trim();
   }
 
diff --git a/extensions/line/src/outbound-media.ts b/extensions/line/src/outbound-media.ts
index 88eab9317da..1bcb5ba79a6 100644
--- a/extensions/line/src/outbound-media.ts
+++ b/extensions/line/src/outbound-media.ts
@@ -1,3 +1,5 @@
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
+
 export type LineOutboundMediaKind = "image" | "video" | "audio";
 
 export type LineOutboundMediaResolved = {
@@ -31,7 +33,7 @@ export function validateLineMediaUrl(url: string): void {
 }
 
 export function detectLineMediaKind(mimeType: string): LineOutboundMediaKind {
-  const normalized = mimeType.toLowerCase();
+  const normalized = normalizeLowercaseStringOrEmpty(mimeType);
   if (normalized.startsWith("image/")) {
     return "image";
   }
@@ -54,7 +56,7 @@ function isHttpsUrl(url: string): boolean {
 
 function detectLineMediaKindFromUrl(url: string): LineOutboundMediaKind | undefined {
   try {
-    const pathname = new URL(url).pathname.toLowerCase();
+    const pathname = normalizeLowercaseStringOrEmpty(new URL(url).pathname);
     if (/\.(png|jpe?g|gif|webp|bmp|heic|heif|avif)$/i.test(pathname)) {
       return "image";
     }
diff --git a/extensions/line/src/reply-payload-transform.ts b/extensions/line/src/reply-payload-transform.ts
index 7375592cd3d..85f88e57420 100644
--- a/extensions/line/src/reply-payload-transform.ts
+++ b/extensions/line/src/reply-payload-transform.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import type { ReplyPayload } from "../runtime-api.js";
 import {
   createAgendaCard,
@@ -33,8 +34,7 @@ export function parseLineDirectives(payload: ReplyPayload): ReplyPayload {
     ...(result.channelData?.line as LineChannelData | undefined),
   };
   const toSlug = (value: string): string =>
-    value
-      .toLowerCase()
+    normalizeLowercaseStringOrEmpty(value)
       .replace(/[^a-z0-9]+/g, "_")
       .replace(/^_+|_+$/g, "") || "device";
   const lineActionData = (action: string, extras?: Record<string, string>): string => {
@@ -85,10 +85,10 @@ export function parseLineDirectives(payload: ReplyPayload): ReplyPayload {
       const [question, yesPart, noPart] = parts;
       const [yesLabel, yesData] = yesPart.includes(":")
         ? yesPart.split(":").map((s) => s.trim())
-        : [yesPart, yesPart.toLowerCase()];
+        : [yesPart, normalizeLowercaseStringOrEmpty(yesPart)];
       const [noLabel, noData] = noPart.includes(":")
         ? noPart.split(":").map((s) => s.trim())
-        : [noPart, noPart.toLowerCase()];
+        : [noPart, normalizeLowercaseStringOrEmpty(noPart)];
 
       lineData.templateMessage = {
         type: "confirm",
@@ -116,7 +116,7 @@ export function parseLineDirectives(payload: ReplyPayload): ReplyPayload {
           if (index === -1) {
             return -1;
           }
-          const lower = trimmed.toLowerCase();
+          const lower = normalizeLowercaseStringOrEmpty(trimmed);
           if (lower.startsWith("http://") || lower.startsWith("https://")) {
             return -1;
           }
@@ -161,7 +161,7 @@ export function parseLineDirectives(payload: ReplyPayload): ReplyPayload {
     const parts = mediaPlayerMatch[1].split("|").map((s) => s.trim());
     if (parts.length >= 1) {
       const [title, artist, source, imageUrl, statusStr] = parts;
-      const isPlaying = statusStr?.toLowerCase() === "playing";
+      const isPlaying = normalizeLowercaseStringOrEmpty(statusStr) === "playing";
       const validImageUrl = imageUrl?.startsWith("https://") ? imageUrl : undefined;
       const deviceKey = toSlug(source || title || "media");
       const card = createMediaPlayerCard({
@@ -281,7 +281,7 @@ export function parseLineDirectives(payload: ReplyPayload): ReplyPayload {
       const controls = controlsStr
         ? controlsStr.split(",").map((ctrlStr) => {
             const [label, data] = ctrlStr.split(":").map((s) => s.trim());
-            const action = data || label.toLowerCase().replace(/\s+/g, "_");
+            const action = data || normalizeLowercaseStringOrEmpty(label).replace(/\s+/g, "_");
             return { label, data: lineActionData(action, { "line.device": deviceKey }) };
           })
         : [];
diff --git a/extensions/line/src/rich-menu.ts b/extensions/line/src/rich-menu.ts
index ed4872d3991..f344b78c354 100644
--- a/extensions/line/src/rich-menu.ts
+++ b/extensions/line/src/rich-menu.ts
@@ -2,6 +2,7 @@ import { readFile } from "node:fs/promises";
 import { messagingApi } from "@line/bot-sdk";
 import { loadConfig } from "openclaw/plugin-sdk/config-runtime";
 import { logVerbose } from "openclaw/plugin-sdk/runtime-env";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { resolveLineAccount } from "./accounts.js";
 import { datetimePickerAction, messageAction, postbackAction, uriAction } from "./actions.js";
 import { resolveLineChannelAccessToken } from "./channel-access-token.js";
@@ -104,7 +105,9 @@ export async function uploadRichMenuImage(
   const blobClient = getBlobClient(opts);
 
   const imageData = await readFile(imagePath);
-  const contentType = imagePath.toLowerCase().endsWith(".png") ? "image/png" : "image/jpeg";
+  const contentType = normalizeLowercaseStringOrEmpty(imagePath).endsWith(".png")
+    ? "image/png"
+    : "image/jpeg";
 
   await blobClient.setRichMenuImage(richMenuId, new Blob([imageData], { type: contentType }));
 
diff --git a/extensions/qqbot/src/gateway.ts b/extensions/qqbot/src/gateway.ts
index b185b3a6265..e40ea89a04c 100644
--- a/extensions/qqbot/src/gateway.ts
+++ b/extensions/qqbot/src/gateway.ts
@@ -1,5 +1,6 @@
 import path from "node:path";
 import type { OpenClawConfig } from "openclaw/plugin-sdk/config-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import WebSocket from "ws";
 import {
   clearTokenCache,
@@ -242,10 +243,11 @@ export async function startGateway(ctx: GatewayContext): Promise<void> {
       return;
     }
 
-    const contentLower = content.toLowerCase();
+    const contentLower = normalizeLowercaseStringOrEmpty(content);
     const isUrgentCommand = URGENT_COMMANDS.some(
       (cmd) =>
-        contentLower === cmd.toLowerCase() || contentLower.startsWith(cmd.toLowerCase() + " "),
+        contentLower === normalizeLowercaseStringOrEmpty(cmd) ||
+        contentLower.startsWith(normalizeLowercaseStringOrEmpty(cmd) + " "),
     );
     if (isUrgentCommand) {
       log?.info(
diff --git a/extensions/qqbot/src/outbound-deliver.ts b/extensions/qqbot/src/outbound-deliver.ts
index 3340561ef8d..b1445f9976c 100644
--- a/extensions/qqbot/src/outbound-deliver.ts
+++ b/extensions/qqbot/src/outbound-deliver.ts
@@ -6,6 +6,7 @@
  * 2. `sendPlainReply` handles plain replies, including markdown images and mixed text/media.
  */
 
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import {
   sendC2CMessage,
   sendDmMessage,
@@ -151,7 +152,7 @@ export async function parseAndSendMediaTags(
 
   const tagCounts = mediaTagMatches.reduce(
     (acc, m) => {
-      const t = m[1].toLowerCase();
+      const t = normalizeLowercaseStringOrEmpty(m[1]);
       acc[t] = (acc[t] ?? 0) + 1;
       return acc;
     },
@@ -184,7 +185,7 @@ export async function parseAndSendMediaTags(
       sendQueue.push({ type: "text", content: filterInternalMarkers(textBefore) });
     }
 
-    const tagName = match[1].toLowerCase();
+    const tagName = normalizeLowercaseStringOrEmpty(match[1]);
     let mediaPath = decodeMediaPath(match[2]?.trim() ?? "", log, prefix);
 
     if (mediaPath) {
diff --git a/extensions/qqbot/src/outbound.ts b/extensions/qqbot/src/outbound.ts
index 1d4b77f8bb2..09e38c0eff0 100644
--- a/extensions/qqbot/src/outbound.ts
+++ b/extensions/qqbot/src/outbound.ts
@@ -1,5 +1,6 @@
 import * as path from "path";
 import { formatErrorMessage } from "openclaw/plugin-sdk/error-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import {
   getAccessToken,
   sendC2CFileMessage,
@@ -303,7 +304,7 @@ export async function sendPhoto(
       return { channel: "qqbot", error: sizeCheck.error! };
     }
     const fileBuffer = await readFileAsync(mediaPath);
-    const ext = path.extname(mediaPath).toLowerCase();
+    const ext = normalizeLowercaseStringOrEmpty(path.extname(mediaPath));
     const mimeTypes: Record<string, string> = {
       ".jpg": "image/jpeg",
       ".jpeg": "image/jpeg",
@@ -482,7 +483,7 @@ async function sendVoiceFromLocal(
   const needsTranscode = shouldTranscodeVoice(mediaPath);
 
   if (needsTranscode && !transcodeEnabled) {
-    const ext = path.extname(mediaPath).toLowerCase();
+    const ext = normalizeLowercaseStringOrEmpty(path.extname(mediaPath));
     debugLog(
       `${prefix} sendVoice: transcode disabled, format ${ext} needs transcode, returning error for fallback`,
     );
@@ -886,7 +887,7 @@ export async function sendText(ctx: OutboundContext): Promise<OutboundResult> {
         sendQueue.push({ type: "text", content: textBefore });
       }
 
-      const tagName = match[1].toLowerCase();
+      const tagName = normalizeLowercaseStringOrEmpty(match[1]);
 
       let mediaPath = match[2]?.trim() ?? "";
       if (mediaPath.startsWith("MEDIA:")) {
@@ -1368,7 +1369,7 @@ async function sendTextAfterMedia(ctx: MediaTargetContext, text: string): Promis
 /** Extract a lowercase extension from a path or URL, ignoring query and hash segments. */
 function getCleanExt(filePath: string): string {
   const cleanPath = filePath.split("?")[0].split("#")[0];
-  return path.extname(cleanPath).toLowerCase();
+  return normalizeLowercaseStringOrEmpty(path.extname(cleanPath));
 }
 
 /** Check whether a file is an image using MIME first and extension as fallback. */
diff --git a/extensions/qqbot/src/slash-commands.ts b/extensions/qqbot/src/slash-commands.ts
index fd63e81821b..f976919b8dc 100644
--- a/extensions/qqbot/src/slash-commands.ts
+++ b/extensions/qqbot/src/slash-commands.ts
@@ -11,6 +11,7 @@ import fs from "node:fs";
 import { createRequire } from "node:module";
 import path from "node:path";
 import { resolveRuntimeServiceVersion } from "openclaw/plugin-sdk/cli-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import type { QQBotAccountConfig } from "./types.js";
 import { debugLog } from "./utils/debug-log.js";
 import { getHomeDir, getQQBotDataDir, isWindows } from "./utils/platform.js";
@@ -134,9 +135,9 @@ const frameworkCommands: Map<string, SlashCommand> = new Map();
 
 function registerCommand(cmd: SlashCommand): void {
   if (cmd.requireAuth) {
-    frameworkCommands.set(cmd.name.toLowerCase(), cmd);
+    frameworkCommands.set(normalizeLowercaseStringOrEmpty(cmd.name), cmd);
   } else {
-    commands.set(cmd.name.toLowerCase(), cmd);
+    commands.set(normalizeLowercaseStringOrEmpty(cmd.name), cmd);
   }
 }
 
@@ -604,7 +605,9 @@ export async function matchSlashCommand(ctx: SlashCommandContext): Promise<Slash
 
   // Parse the command name and trailing arguments.
   const spaceIdx = content.indexOf(" ");
-  const cmdName = (spaceIdx === -1 ? content.slice(1) : content.slice(1, spaceIdx)).toLowerCase();
+  const cmdName = normalizeLowercaseStringOrEmpty(
+    spaceIdx === -1 ? content.slice(1) : content.slice(1, spaceIdx),
+  );
   const args = spaceIdx === -1 ? "" : content.slice(spaceIdx + 1).trim();
 
   const cmd = commands.get(cmdName);
diff --git a/extensions/qqbot/src/utils/audio-convert.ts b/extensions/qqbot/src/utils/audio-convert.ts
index 36537d9844d..6d2d86a04ec 100644
--- a/extensions/qqbot/src/utils/audio-convert.ts
+++ b/extensions/qqbot/src/utils/audio-convert.ts
@@ -117,7 +117,7 @@ export function isVoiceAttachment(att: { content_type?: string; filename?: strin
   if (att.content_type === "voice" || att.content_type?.startsWith("audio/")) {
     return true;
   }
-  const ext = att.filename ? path.extname(att.filename).toLowerCase() : "";
+  const ext = att.filename ? normalizeLowercaseStringOrEmpty(path.extname(att.filename)) : "";
   return [".amr", ".silk", ".slk", ".slac"].includes(ext);
 }
 
@@ -139,7 +139,7 @@ export function isAudioFile(filePath: string, mimeType?: string): boolean {
       return true;
     }
   }
-  const ext = path.extname(filePath).toLowerCase();
+  const ext = normalizeLowercaseStringOrEmpty(path.extname(filePath));
   return [
     ".silk",
     ".slk",
@@ -175,10 +175,10 @@ const QQ_NATIVE_VOICE_EXTS = new Set([".silk", ".slk", ".amr", ".wav", ".mp3"]);
  */
 export function shouldTranscodeVoice(filePath: string, mimeType?: string): boolean {
   // Prefer MIME when it is available.
-  if (mimeType && QQ_NATIVE_VOICE_MIMES.has(mimeType.toLowerCase())) {
+  if (mimeType && QQ_NATIVE_VOICE_MIMES.has(normalizeLowercaseStringOrEmpty(mimeType))) {
     return false;
   }
-  const ext = path.extname(filePath).toLowerCase();
+  const ext = normalizeLowercaseStringOrEmpty(path.extname(filePath));
   if (QQ_NATIVE_VOICE_EXTS.has(ext)) {
     return false;
   }
@@ -510,7 +510,7 @@ export async function audioFileToSilkBase64(
     return null;
   }
 
-  const ext = path.extname(filePath).toLowerCase();
+  const ext = normalizeLowercaseStringOrEmpty(path.extname(filePath));
 
   const uploadFormats = directUploadFormats
     ? normalizeFormats(directUploadFormats)
diff --git a/extensions/qqbot/src/utils/file-utils.ts b/extensions/qqbot/src/utils/file-utils.ts
index cbd6a4c9db6..eec3b768dd4 100644
--- a/extensions/qqbot/src/utils/file-utils.ts
+++ b/extensions/qqbot/src/utils/file-utils.ts
@@ -4,6 +4,7 @@ import * as path from "node:path";
 import { formatErrorMessage } from "openclaw/plugin-sdk/error-runtime";
 import { fetchRemoteMedia } from "openclaw/plugin-sdk/media-runtime";
 import type { SsrFPolicy } from "openclaw/plugin-sdk/ssrf-runtime";
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 
 /** Maximum file size accepted by the QQ Bot API. */
 export const MAX_UPLOAD_SIZE = 20 * 1024 * 1024;
@@ -92,7 +93,7 @@ export function formatFileSize(bytes: number): string {
 
 /** Infer a MIME type from the file extension. */
 export function getMimeType(filePath: string): string {
-  const ext = path.extname(filePath).toLowerCase();
+  const ext = normalizeLowercaseStringOrEmpty(path.extname(filePath));
   const mimeTypes: Record<string, string> = {
     ".jpg": "image/jpeg",
     ".jpeg": "image/jpeg",
diff --git a/extensions/qqbot/src/utils/media-tags.ts b/extensions/qqbot/src/utils/media-tags.ts
index 94ee1d2b038..1940f504ff2 100644
--- a/extensions/qqbot/src/utils/media-tags.ts
+++ b/extensions/qqbot/src/utils/media-tags.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import { expandTilde } from "./platform.js";
 
 // Canonical media tags. `qqmedia` is the generic auto-routing tag.
@@ -84,7 +85,7 @@ const FUZZY_MEDIA_TAG_REGEX = new RegExp(
 
 /** Normalize a raw tag name into the canonical tag set. */
 function resolveTagName(raw: string): (typeof VALID_TAGS)[number] {
-  const lower = raw.toLowerCase();
+  const lower = normalizeLowercaseStringOrEmpty(raw);
   if ((VALID_TAGS as readonly string[]).includes(lower)) {
     return lower as (typeof VALID_TAGS)[number];
   }
diff --git a/extensions/qqbot/src/utils/text-parsing.ts b/extensions/qqbot/src/utils/text-parsing.ts
index c77eda58829..5ebaa117d63 100644
--- a/extensions/qqbot/src/utils/text-parsing.ts
+++ b/extensions/qqbot/src/utils/text-parsing.ts
@@ -1,3 +1,4 @@
+import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import type { RefAttachmentSummary } from "../ref-index-store.js";
 
 /** Replace QQ face tags with readable text labels. */
@@ -62,7 +63,7 @@ export function buildAttachmentSummaries(
     return undefined;
   }
   return attachments.map((att, idx) => {
-    const ct = att.content_type?.toLowerCase() ?? "";
+    const ct = normalizeLowercaseStringOrEmpty(att.content_type);
     let type: RefAttachmentSummary["type"] = "unknown";
     if (ct.startsWith("image/")) {
       type = "image";
diff --git a/extensions/slack/src/monitor/allow-list.ts b/extensions/slack/src/monitor/allow-list.ts
index 56a5e5aca7d..cb43d7956d3 100644
--- a/extensions/slack/src/monitor/allow-list.ts
+++ b/extensions/slack/src/monitor/allow-list.ts
@@ -59,8 +59,8 @@ export function resolveSlackAllowListMatch(params: {
   allowNameMatching?: boolean;
 }): SlackAllowListMatch {
   const compiledAllowList = compileAllowlist(params.allowList);
-  const id = params.id?.toLowerCase();
-  const name = params.name?.toLowerCase();
+  const id = normalizeOptionalLowercaseString(params.id);
+  const name = normalizeOptionalLowercaseString(params.name);
   const slug = normalizeSlackSlug(name);
   const candidates: Array<{ value?: string; source: SlackAllowListSource }> = [
     { value: id, source: "id" },
diff --git a/extensions/slack/src/monitor/media.ts b/extensions/slack/src/monitor/media.ts
index d58e356a3b9..40882e932c8 100644
--- a/extensions/slack/src/monitor/media.ts
+++ b/extensions/slack/src/monitor/media.ts
@@ -5,7 +5,10 @@ import type { FetchLike } from "openclaw/plugin-sdk/media-runtime";
 import { fetchRemoteMedia } from "openclaw/plugin-sdk/media-runtime";
 import { saveMediaBuffer } from "openclaw/plugin-sdk/media-runtime";
 import { resolveRequestUrl } from "openclaw/plugin-sdk/request-url";
-import { normalizeOptionalLowercaseString } from "openclaw/plugin-sdk/text-runtime";
+import {
+  normalizeLowercaseStringOrEmpty,
+  normalizeOptionalLowercaseString,
+} from "openclaw/plugin-sdk/text-runtime";
 import type { SlackAttachment, SlackFile } from "../types.js";
 
 function isSlackHostname(hostname: string): boolean {
@@ -135,7 +138,9 @@ function resolveSlackMediaMimetype(
 }
 
 function looksLikeHtmlBuffer(buffer: Buffer): boolean {
-  const head = buffer.subarray(0, 512).toString("utf-8").replace(/^\s+/, "").toLowerCase();
+  const head = normalizeLowercaseStringOrEmpty(
+    buffer.subarray(0, 512).toString("utf-8").replace(/^\s+/, ""),
+  );
   return head.startsWith("<!doctype html") || head.startsWith("<html");
 }
 
@@ -235,8 +240,8 @@ export async function resolveSlackMedia(params: {
 
         // Guard against auth/login HTML pages returned instead of binary media.
         // Allow user-provided HTML files through.
-        const fileMime = file.mimetype?.toLowerCase();
-        const fileName = file.name?.toLowerCase() ?? "";
+        const fileMime = normalizeOptionalLowercaseString(file.mimetype);
+        const fileName = normalizeLowercaseStringOrEmpty(file.name);
         const isExpectedHtml =
           fileMime === "text/html" || fileName.endsWith(".html") || fileName.endsWith(".htm");
         if (!isExpectedHtml) {
diff --git a/extensions/slack/src/monitor/slash.ts b/extensions/slack/src/monitor/slash.ts
index f482c027ba3..7c8733256a9 100644
--- a/extensions/slack/src/monitor/slash.ts
+++ b/extensions/slack/src/monitor/slash.ts
@@ -771,7 +771,7 @@ export async function registerSlackMonitorSlashCommands(params: {
       }
       const query = normalizeLowercaseStringOrEmpty(typedBody.value);
       const options = entry.choices
-        .filter((choice) => !query || choice.label.toLowerCase().includes(query))
+        .filter((choice) => !query || normalizeLowercaseStringOrEmpty(choice.label).includes(query))
         .slice(0, SLACK_COMMAND_ARG_SELECT_OPTIONS_MAX)
         .map((choice) => ({
           text: { type: "plain_text", text: choice.label.slice(0, 75) },