diff --git a/src/SettingConfig.ts b/src/SettingConfig.ts
index 944f911..30fff18 100644
--- a/src/SettingConfig.ts
+++ b/src/SettingConfig.ts
@@ -65,11 +65,11 @@ export const read_setting_from_file = ()=>{
 export function get_setting():SettingConfig{
     if(setting === null){
         setting = read_setting_from_file();
-        const env = process.env.NODE_ENV || 'development';
-        if(env != "production" && env != "development"){
+        const env = process.env.NODE_ENV;
+        if(env !== undefined && (env != "production" && env != "development")){
             throw new Error("process unknown value in NODE_ENV: must be either \"development\" or \"production\"");
         }
-        setting.mode = env || setting.mode;
+        setting.mode = env ?? setting.mode;
     }
     return setting;
 }
diff --git a/src/client/component/contentinfo.tsx b/src/client/component/contentinfo.tsx
index 4c42665..d858a62 100644
--- a/src/client/component/contentinfo.tsx
+++ b/src/client/component/contentinfo.tsx
@@ -90,31 +90,31 @@ export const ContentInfo = (props: {
     const classes = useStyles();
     const theme = useTheme();
     const document = props.document;
-    const propclasses = props.classes || {};
+    const propclasses = props.classes ?? {};
     const rootName = props.short ? classes.short_root : classes.root;
     const thumbnail_anchor = props.short ? classes.short_thumbnail_anchor : "";
     const thumbnail_content = props.short ? classes.short_thumbnail_content :
         classes.thumbnail_content;
     const subinfoContainer = props.short ? classes.short_subinfoContainer :
         classes.subinfoContainer;
-    return (<Paper className={propclasses.root || rootName} elevation={4}>
-        <Link className={propclasses.thumbnail_anchor || thumbnail_anchor} component={RouterLink} to={{
+    return (<Paper className={propclasses.root ?? rootName} elevation={4}>
+        <Link className={propclasses.thumbnail_anchor ?? thumbnail_anchor} component={RouterLink} to={{
             pathname:makeContentReaderUrl(document.id)
         }}>
             {document.deleted_at === null ? 
             (<ThumbnailContainer content={document} 
-                className={propclasses.thumbnail_content || thumbnail_content}/>)
-            : (<Typography className={propclasses.thumbnail_content || thumbnail_content} variant='h4'>Deleted</Typography>)}
+                className={propclasses.thumbnail_content ?? thumbnail_content}/>)
+            : (<Typography className={propclasses.thumbnail_content ?? thumbnail_content} variant='h4'>Deleted</Typography>)}
         </Link>
-        <Box className={propclasses.infoContainer || classes.infoContainer}>
+        <Box className={propclasses.infoContainer ?? classes.infoContainer}>
             <Link variant='h5' color='inherit' component={RouterLink} to={{
                 pathname: props.gallery === undefined ? makeContentReaderUrl(document.id) : makeContentInfoUrl(document.id),
             }}
-                className={propclasses.title || classes.title}>
+                className={propclasses.title ?? classes.title}>
                 {document.title}
             </Link>
-            <Box className={propclasses.subinfoContainer || subinfoContainer}>
-                {props.short ? (<Box className={propclasses.tag_list || classes.tag_list}>{document.tags.map(x => 
+            <Box className={propclasses.subinfoContainer ?? subinfoContainer}>
+                {props.short ? (<Box className={propclasses.tag_list ?? classes.tag_list}>{document.tags.map(x => 
                                 (<TagChip key={x} label={x} clickable tagname={x} size="small"></TagChip>)
                             )}</Box>) : (
                     <ComicDetailTag tags={document.tags} classes={({tag_list:classes.tag_list})}></ComicDetailTag>)
diff --git a/src/client/component/headline.tsx b/src/client/component/headline.tsx
index f33c339..1d776b8 100644
--- a/src/client/component/headline.tsx
+++ b/src/client/component/headline.tsx
@@ -201,8 +201,8 @@ export const Headline = (prop: {
                 </Drawer>
             </Hidden>
         </nav>
-        <main className={prop.classes?.content || classes.content}>
-            <div className={prop.classes?.toolbar || classes.toolbar}></div>
+        <main className={prop.classes?.content ?? classes.content}>
+            <div className={prop.classes?.toolbar ?? classes.toolbar}></div>
             {prop.children}
         </main>
     </div>);
diff --git a/src/client/component/navlist.tsx b/src/client/component/navlist.tsx
index 8ca037a..efa8497 100644
--- a/src/client/component/navlist.tsx
+++ b/src/client/component/navlist.tsx
@@ -28,7 +28,7 @@ export const BackItem = (props:{to?:string})=>{
 }
 
 export function CommonMenuList(props?:{url?:string}) {
-    let url = props?.url || "";
+    let url = props?.url ?? "";
     return (<NavList>
         {url !== "" && <><BackItem /> <Divider /></>}
         <NavItem name="All" to="/" icon={<HomeIcon />} />
diff --git a/src/client/component/tagchip.tsx b/src/client/component/tagchip.tsx
index f2cd2cf..1b47bbe 100644
--- a/src/client/component/tagchip.tsx
+++ b/src/client/component/tagchip.tsx
@@ -81,8 +81,8 @@ export const TagChip = (props:TagChipProp)=>{
         }
     }
     const inner = clickable ? 
-    (<ColorChip color={getTagColorName(tagname)} clickable={clickable} label={newlabel||label} {...rest} 
+    (<ColorChip color={getTagColorName(tagname)} clickable={clickable} label={newlabel??label} {...rest} 
     component={RouterLink} to={`/search?allow_tag=${tagname}`}></ColorChip>):
-    (<ColorChip color={getTagColorName(tagname)} clickable={clickable} label={newlabel||label} {...rest}></ColorChip>);
+    (<ColorChip color={getTagColorName(tagname)} clickable={clickable} label={newlabel??label} {...rest}></ColorChip>);
     return inner;
 }
\ No newline at end of file
diff --git a/src/client/page/gallery.tsx b/src/client/page/gallery.tsx
index 7762d82..2f228f1 100644
--- a/src/client/page/gallery.tsx
+++ b/src/client/page/gallery.tsx
@@ -36,7 +36,7 @@ export const GalleryInfo = (props: GalleryProp)=>{
         load();
     },[props.diff]);
     const classes = useStyles();
-    const queryString = toQueryString(props.option||{});
+    const queryString = toQueryString(props.option??{});
 
     if(state.documents === undefined){
         return (<LoadingCircle/>);
diff --git a/src/content/comic.ts b/src/content/comic.ts
index e245954..74e3772 100644
--- a/src/content/comic.ts
+++ b/src/content/comic.ts
@@ -45,11 +45,11 @@ export class ComicReferrer extends createDefaultClass("comic"){
         if(this.desc === undefined){
             return basebody;
         }
-        let tags:string[] = this.desc.tags || [];
-        tags = tags.concat(this.desc.artist?.map(x=>`artist:${x}`) || []);
-        tags = tags.concat(this.desc.character?.map(x=>`character:${x}`) || []);
-        tags = tags.concat(this.desc.group?.map(x=>`group:${x}`) || []);
-        tags = tags.concat(this.desc.series?.map(x=>`series:${x}`) || []);
+        let tags:string[] = this.desc.tags ?? [];
+        tags = tags.concat(this.desc.artist?.map(x=>`artist:${x}`) ?? []);
+        tags = tags.concat(this.desc.character?.map(x=>`character:${x}`) ?? []);
+        tags = tags.concat(this.desc.group?.map(x=>`group:${x}`) ?? []);
+        tags = tags.concat(this.desc.series?.map(x=>`series:${x}`) ?? []);
         const type = this.desc.type instanceof Array ? this.desc.type[0]: this.desc.type;
         tags.push(`type:${type}`);
         return {
diff --git a/src/content/file.ts b/src/content/file.ts
index bad6edc..06a15a9 100644
--- a/src/content/file.ts
+++ b/src/content/file.ts
@@ -38,7 +38,7 @@ export const createDefaultClass = (type:string):ContentFileConstructor=>{
                 content_type: cons.content_type,
                 filename: base,
                 tags: [],
-                content_hash: this.hash || await this.getHash(),
+                content_hash: this.hash ?? await this.getHash(),
             } as DocumentBody;
             return ret;
         }
diff --git a/src/db/doc.ts b/src/db/doc.ts
index 4448352..2c0fc0f 100644
--- a/src/db/doc.ts
+++ b/src/db/doc.ts
@@ -69,12 +69,12 @@ class KnexDocumentAccessor implements DocumentAccessor{
         }));
     }
     async findList(option?:QueryListOption){
-        option = option || {};
-        const allow_tag = option.allow_tag || [];
-        const eager_loading = typeof option.eager_loading === "undefined" || option.eager_loading;
-        const limit = option.limit || 20;
-        const use_offset = option.use_offset || false;
-        const offset = option.offset || 0;
+        option = option ?? {};
+        const allow_tag = option.allow_tag ?? [];
+        const eager_loading = option.eager_loading ?? true;
+        const limit = option.limit ?? 20;
+        const use_offset = option.use_offset ?? false;
+        const offset = option.offset ?? 0;
         const word = option.word;
         const content_type = option.content_type;
         const cursor = option.cursor;
@@ -134,6 +134,9 @@ class KnexDocumentAccessor implements DocumentAccessor{
                 idmap[id].tags.push(tag_name);
             }
         }
+        else{
+            result.forEach(v=>{v.tags = [];});
+        }
         return result;
     };
     async findByPath(path:string,filename?:string):Promise<Document[]>{
diff --git a/src/db/tag.ts b/src/db/tag.ts
index 8e24c70..4cf3d31 100644
--- a/src/db/tag.ts
+++ b/src/db/tag.ts
@@ -12,7 +12,7 @@ class KnexTagAccessor implements TagAccessor{
         this.knex = knex;
     }
     async getTagAllList(onlyname?:boolean){
-        onlyname = onlyname || false;
+        onlyname = onlyname ?? false;
         const t:DBTags[] = await this.knex.select(onlyname ? "*" : "name").from("tags")
         return t;
     }
diff --git a/src/diff/watcher/recursive_watcher.ts b/src/diff/watcher/recursive_watcher.ts
index d77e3cb..88ef23d 100644
--- a/src/diff/watcher/recursive_watcher.ts
+++ b/src/diff/watcher/recursive_watcher.ts
@@ -22,19 +22,19 @@ export class RecursiveWatcher extends EventEmitter implements IDiffWatcher  {
     readonly path: string;
     private watcher: FSWatcher
 
-    constructor(path:string, option?:RecursiveWatcherOption){
+    constructor(path:string, option:RecursiveWatcherOption = {
+        watchDir:false,
+        watchFile:true,
+    }){
         super();
         this.path = path;
-        option = option || {
-            watchDir:false,
-            watchFile:true,
-        }
         this.watcher = watch(path,{
             persistent:true,
             ignoreInitial:true,
             depth:100,
         });
-        if(option.watchFile === undefined || option.watchFile){
+        option.watchFile ??= true;
+        if(option.watchFile){
             this.watcher.on("add",path=>{
                 const cpath = join(this.path,path);
                 this.emit("create",cpath);
diff --git a/src/route/all.ts b/src/route/all.ts
index d99c3f7..543e3ba 100644
--- a/src/route/all.ts
+++ b/src/route/all.ts
@@ -24,7 +24,7 @@ const all_middleware = (cont: string|undefined, restarg: string|undefined)=>asyn
         ctx.status = 404;
         return;
     }
-    const rest = "/"+(restarg || "");
+    const rest = "/"+(restarg ?? "");
     const result = router.match(rest,"GET");
     if(!result.route){
         return await next();
diff --git a/src/route/contents.ts b/src/route/contents.ts
index 43a8bb7..c8c0b3b 100644
--- a/src/route/contents.ts
+++ b/src/route/contents.ts
@@ -25,7 +25,7 @@ const ContentTagIDHandler = (controller: DocumentAccessor) => async (ctx: Contex
     if (document == undefined){
         return sendError(404,"document does not exist.");
     }
-    ctx.body = document.tags || [];
+    ctx.body = document.tags;
     ctx.type = 'json';
 };
 const ContentQueryHandler = (controller : DocumentAccessor) => async (ctx: Context,next: Next)=>{
diff --git a/src/route/error_handler.ts b/src/route/error_handler.ts
index be43a02..3cc0a76 100644
--- a/src/route/error_handler.ts
+++ b/src/route/error_handler.ts
@@ -31,7 +31,7 @@ export const error_handler = async (ctx:Context,next: Next)=>{
         if(err instanceof ClientRequestError){
             const body : ErrorFormat= {
                 code: err.code,
-                message: code_to_message_table[err.code] || "",
+                message: code_to_message_table[err.code] ?? "",
                 detail: err.message
             }
             ctx.status = err.code;
@@ -44,7 +44,7 @@ export const error_handler = async (ctx:Context,next: Next)=>{
 }
 
 export const sendError = (code:number,message?:string) =>{
-    throw new ClientRequestError(code,message || "");
+    throw new ClientRequestError(code,message ?? "");
 }
 
 export default error_handler;
\ No newline at end of file
diff --git a/src/route/util.ts b/src/route/util.ts
index a7aa7e3..9eb12df 100644
--- a/src/route/util.ts
+++ b/src/route/util.ts
@@ -7,7 +7,7 @@ export function ParseQueryNumber(s: string|undefined): number| undefined{
     else return Number.parseInt(s);
 }
 export function ParseQueryArray(s: string[]|string|undefined){
-    s = s || [];
+    s = s ?? [];
     const r = s instanceof Array ? s : [s];
     return r.map(x=>decodeURIComponent(x));
 }