diff --git a/.eslintrc.js b/.eslintrc.js
index 1477adfb4e..d395941f2a 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -44,11 +44,7 @@ module.exports = {
   plugins: ["import"],
   parser: vueEslintParser,
   parserOptions: vueEslintParserOptions,
-  ignorePatterns: [
-    "dist/**/*",
-    "dist_*/**/*",
-    "node_modules/**/*",
-  ],
+  ignorePatterns: ["dist/**/*", "dist_*/**/*", "node_modules/**/*"],
   rules: {
     "linebreak-style":
       process.env.NODE_ENV === "production" && process.platform !== "win32"
@@ -63,17 +59,6 @@ module.exports = {
         endOfLine: "auto",
       },
     ],
-    "vue/no-restricted-syntax": [
-      "error",
-      {
-        selector: "LogicalExpression[operator=??]",
-        message: `template内で"??"を使うとgithubのsyntax highlightが崩れるので\n三項演算子等を使って書き換えてください`,
-      },
-      {
-        selector: "MemberExpression[optional=true]",
-        message: `template内で"?."を使うとgithubのsyntax highlightが崩れるので\n三項演算子等を使って書き換えてください`,
-      },
-    ],
     "@typescript-eslint/no-unused-vars": [
       process.env.NODE_ENV === "development" ? "warn" : "error", // 開発時のみwarn
       {
diff --git a/src/components/Dialog/HelpDialog/HelpLibraryPolicySection.vue b/src/components/Dialog/HelpDialog/HelpLibraryPolicySection.vue
index 87675f6f9f..41d5e7f407 100644
--- a/src/components/Dialog/HelpDialog/HelpLibraryPolicySection.vue
+++ b/src/components/Dialog/HelpDialog/HelpLibraryPolicySection.vue
@@ -12,13 +12,13 @@
           >
             <!-- エンジンが一つだけの場合は名前を表示しない -->
             <h2 v-if="engineInfos.size > 1" class="subtitle">
-              {{ mapNullablePipe(engineInfos.get(engineId), (v) => v.name) }}
+              {{ engineInfos.get(engineId)?.name }}
             </h2>
             <BaseRowCard
-              v-for="([, characterInfo], characterIndex) in mapNullablePipe(
-                engineInfos.get(engineId),
-                (v) => v.characterInfos,
-              )"
+              v-for="([, characterInfo], characterIndex) in getOrThrow(
+                engineInfos,
+                engineId,
+              ).characterInfos"
               :key="characterIndex"
               :title="characterInfo.metas.speakerName"
               clickable
@@ -49,12 +49,10 @@
         </div>
         <h1 class="title">
           {{
-            mapNullablePipe(
-              engineInfos.get(selectedInfo.engine),
-              (v) => v.characterInfos,
-              (v) => mapNullablePipe(selectedInfo, (i) => v.get(i.character)),
-              (v) => v.metas.speakerName,
-            )
+            selectedInfo &&
+            engineInfos
+              .get(selectedInfo.engine)
+              ?.characterInfos.get(selectedInfo.character)?.metas.speakerName
           }}
         </h1>
         <BaseDocumentView>
@@ -75,7 +73,7 @@ import BaseDocumentView from "@/components/Base/BaseDocumentView.vue";
 import { useStore } from "@/store";
 import { useMarkdownIt } from "@/plugins/markdownItPlugin";
 import { EngineId, SpeakerId } from "@/type/preload";
-import { mapNullablePipe } from "@/helpers/map";
+import { getOrThrow } from "@/helpers/mapHelper";
 
 type DetailKey = { engine: EngineId; character: SpeakerId };
 
diff --git a/src/helpers/map.ts b/src/helpers/map.ts
deleted file mode 100644
index def8bbf1cc..0000000000
--- a/src/helpers/map.ts
+++ /dev/null
@@ -1,39 +0,0 @@
-export function mapNullablePipe<T, U1>(
-  source: T | undefined,
-  fn1: (_: NonNullable<T>) => U1 | undefined,
-): U1 | undefined;
-export function mapNullablePipe<T, U1, U2>(
-  source: T | undefined,
-  fn1: (_: NonNullable<T>) => U1 | undefined,
-  fn2: (_: NonNullable<U1>) => U2 | undefined,
-): U2 | undefined;
-export function mapNullablePipe<T, U1, U2, U3>(
-  source: T | undefined,
-  fn1: (_: NonNullable<T>) => U1 | undefined,
-  fn2: (_: NonNullable<U1>) => U2 | undefined,
-  fn3: (_: NonNullable<U2>) => U3 | undefined,
-): U3 | undefined;
-/**
- * 一連の関数を実行する。途中でundefinedかnullを返すとその後undefinedを返す。
- */
-// eslint-disable-next-line @typescript-eslint/ban-types, @typescript-eslint/no-explicit-any
-export function mapNullablePipe(source: any, ...fn: Function[]) {
-  // eslint-disable-next-line @typescript-eslint/no-unsafe-return
-  return fn.reduce((prev, curr) => {
-    if (prev == undefined) {
-      return undefined;
-    }
-    // eslint-disable-next-line @typescript-eslint/no-unsafe-return
-    return curr(prev);
-  }, source);
-}
-
-export const nullableToDefault = <T>(
-  defaultValue: T,
-  maybeValue: T | undefined,
-): T => {
-  if (maybeValue == undefined) {
-    return defaultValue;
-  }
-  return maybeValue;
-};
diff --git a/tests/unit/lib/map.spec.ts b/tests/unit/lib/map.spec.ts
deleted file mode 100644
index 5f891c28c2..0000000000
--- a/tests/unit/lib/map.spec.ts
+++ /dev/null
@@ -1,58 +0,0 @@
-import { describe, expect, it } from "vitest";
-
-import { mapNullablePipe, nullableToDefault } from "@/helpers/map";
-
-type DummyType = {
-  outerValue?: {
-    innerValue?: string;
-  };
-};
-
-describe("mapUndefinedPipe", () => {
-  it("値をunwrap出来る", () => {
-    const key = "test";
-    const innerValue = "value";
-    const value: DummyType = {
-      outerValue: {
-        innerValue,
-      },
-    };
-    const map = new Map<string, DummyType>([[key, value]]);
-    expect(
-      mapNullablePipe(
-        map.get(key),
-        (v) => v.outerValue,
-        (v) => v.innerValue,
-      ),
-    ).toEqual(innerValue);
-  });
-
-  it("途中でundefinedを返すとその後undefinedを返す", () => {
-    const key = "test";
-    const value: DummyType = {
-      outerValue: {
-        innerValue: undefined,
-      },
-    };
-    const map = new Map<string, DummyType>([[key, value]]);
-    expect(
-      mapNullablePipe(
-        map.get(key),
-        (v) => v.outerValue,
-        (v) => v.innerValue,
-      ),
-    ).toBeUndefined();
-  });
-});
-
-describe("undefinedToDefault", () => {
-  it("値がある時はそのまま返す", () => {
-    const actualValue = "value";
-    expect(nullableToDefault("test", actualValue)).toEqual(actualValue);
-  });
-
-  it("値がない時はdefaultValueを返す", () => {
-    const defaultValue = "test";
-    expect(nullableToDefault(defaultValue, undefined)).toEqual(defaultValue);
-  });
-});