diff --git a/eslint.config.mjs b/eslint.config.mjs
index bd12d12c70..ae9cf27460 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -131,6 +131,7 @@ export default [
       "no-sequences": "error",
       "no-shadow": "off",
       "@typescript-eslint/no-shadow": "error",
+      "@typescript-eslint/prefer-optional-chain": "error",
       "one-var": ["error", "never"],
     },
   },
diff --git a/lib/analyze-action.js b/lib/analyze-action.js
index 8b936b19d2..168be4f510 100644
--- a/lib/analyze-action.js
+++ b/lib/analyze-action.js
@@ -91887,13 +91887,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -92273,7 +92273,7 @@ function tryGetTagNameFromUrl(url2, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url2}. Matched ${JSON.stringify(
         match
diff --git a/lib/init-action-post.js b/lib/init-action-post.js
index b2de76f433..5ebaaa8722 100644
--- a/lib/init-action-post.js
+++ b/lib/init-action-post.js
@@ -129872,13 +129872,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -130258,7 +130258,7 @@ function tryGetTagNameFromUrl(url2, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url2}. Matched ${JSON.stringify(
         match
@@ -133655,7 +133655,7 @@ function getInputOrThrow(workflow, jobName, actionName, inputName, matrixVars) {
       input = input.replace(`\${{matrix.${key}}}`, value);
     }
   }
-  if (input !== void 0 && input.includes("${{")) {
+  if (input?.includes("${{")) {
     throw new Error(
       `Could not get ${inputName} input to ${actionName} since it contained an unrecognized dynamic value.`
     );
diff --git a/lib/init-action.js b/lib/init-action.js
index 18e350024c..324b93b6ef 100644
--- a/lib/init-action.js
+++ b/lib/init-action.js
@@ -88036,7 +88036,7 @@ function parseQueriesFromInput(rawQueriesInput, queriesInputCombines, errorToThr
 }
 function combineQueries(logger, config, augmentationProperties) {
   const result = [];
-  if (augmentationProperties.repoPropertyQueries && augmentationProperties.repoPropertyQueries.input) {
+  if (augmentationProperties.repoPropertyQueries?.input) {
     logger.info(
       `Found query configuration in the repository properties (${"github-codeql-extra-queries" /* EXTRA_QUERIES */}): ${augmentationProperties.repoPropertyQueries.input.map((q) => q.uses).join(", ")}`
     );
@@ -89584,7 +89584,7 @@ async function getRemoteConfig(logger, configFile, apiDetails, validateConfig) {
     "(?<owner>[^/]+)/(?<repo>[^/]+)/(?<path>[^@]+)@(?<ref>.*)"
   );
   const pieces = format.exec(configFile);
-  if (pieces === null || pieces.groups === void 0 || pieces.length < 5) {
+  if (pieces?.groups === void 0 || pieces.length < 5) {
     throw new ConfigurationError(
       getConfigFileRepoFormatInvalidMessage(configFile)
     );
@@ -90194,13 +90194,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -90580,7 +90580,7 @@ function tryGetTagNameFromUrl(url, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url}. Matched ${JSON.stringify(
         match
diff --git a/lib/setup-codeql-action.js b/lib/setup-codeql-action.js
index 37fc43ec6d..7434669fc9 100644
--- a/lib/setup-codeql-action.js
+++ b/lib/setup-codeql-action.js
@@ -87151,13 +87151,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -87537,7 +87537,7 @@ function tryGetTagNameFromUrl(url, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url}. Matched ${JSON.stringify(
         match
diff --git a/lib/start-proxy-action-post.js b/lib/start-proxy-action-post.js
index b224695c4b..94c68de174 100644
--- a/lib/start-proxy-action-post.js
+++ b/lib/start-proxy-action-post.js
@@ -118975,7 +118975,7 @@ async function runWrapper() {
       getTemporaryDirectory(),
       logger
     );
-    if (config && config.debugMode || core13.isDebug()) {
+    if (config?.debugMode || core13.isDebug()) {
       const logFilePath = core13.getState("proxy-log-file");
       logger.info(
         "Debug mode is on. Uploading proxy log as Actions debugging artifact..."
diff --git a/lib/upload-lib.js b/lib/upload-lib.js
index a952f35ab4..bb5628b24b 100644
--- a/lib/upload-lib.js
+++ b/lib/upload-lib.js
@@ -89703,13 +89703,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -90089,7 +90089,7 @@ function tryGetTagNameFromUrl(url2, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url2}. Matched ${JSON.stringify(
         match
diff --git a/lib/upload-sarif-action.js b/lib/upload-sarif-action.js
index 9596cc4512..af65a9ee26 100644
--- a/lib/upload-sarif-action.js
+++ b/lib/upload-sarif-action.js
@@ -90376,13 +90376,13 @@ async function getTarVersion() {
   }
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
     return { type: "bsd", version: match[1] };
@@ -90762,7 +90762,7 @@ function tryGetTagNameFromUrl(url2, logger) {
     return void 0;
   }
   const match = matches[matches.length - 1];
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url2}. Matched ${JSON.stringify(
         match
diff --git a/src/config-utils.ts b/src/config-utils.ts
index f523213b1d..3a1d040db0 100644
--- a/src/config-utils.ts
+++ b/src/config-utils.ts
@@ -943,7 +943,7 @@ async function getRemoteConfig(
   );
   const pieces = format.exec(configFile);
   // 5 = 4 groups + the whole expression
-  if (pieces === null || pieces.groups === undefined || pieces.length < 5) {
+  if (pieces?.groups === undefined || pieces.length < 5) {
     throw new ConfigurationError(
       errorMessages.getConfigFileRepoFormatInvalidMessage(configFile),
     );
diff --git a/src/config/db-config.ts b/src/config/db-config.ts
index 16cda3abf3..3293535f39 100644
--- a/src/config/db-config.ts
+++ b/src/config/db-config.ts
@@ -380,10 +380,7 @@ function combineQueries(
   const result: QuerySpec[] = [];
 
   // Query settings obtained from the repository properties have the highest precedence.
-  if (
-    augmentationProperties.repoPropertyQueries &&
-    augmentationProperties.repoPropertyQueries.input
-  ) {
+  if (augmentationProperties.repoPropertyQueries?.input) {
     logger.info(
       `Found query configuration in the repository properties (${RepositoryPropertyName.EXTRA_QUERIES}): ` +
         `${augmentationProperties.repoPropertyQueries.input.map((q) => q.uses).join(", ")}`,
diff --git a/src/setup-codeql.ts b/src/setup-codeql.ts
index 9ee0c4b82a..9488930229 100644
--- a/src/setup-codeql.ts
+++ b/src/setup-codeql.ts
@@ -168,7 +168,7 @@ export function tryGetTagNameFromUrl(
   // assumes less about the structure of the URL.
   const match = matches[matches.length - 1];
 
-  if (match === null || match.length !== 2) {
+  if (match?.length !== 2) {
     logger.debug(
       `Could not determine tag name for URL ${url}. Matched ${JSON.stringify(
         match,
diff --git a/src/start-proxy-action-post.ts b/src/start-proxy-action-post.ts
index 100b8a75ff..5042d5229f 100644
--- a/src/start-proxy-action-post.ts
+++ b/src/start-proxy-action-post.ts
@@ -30,7 +30,7 @@ async function runWrapper() {
       logger,
     );
 
-    if ((config && config.debugMode) || core.isDebug()) {
+    if (config?.debugMode || core.isDebug()) {
       const logFilePath = core.getState("proxy-log-file");
       logger.info(
         "Debug mode is on. Uploading proxy log as Actions debugging artifact...",
diff --git a/src/tar.ts b/src/tar.ts
index 280f3d7f7b..93e9a05548 100644
--- a/src/tar.ts
+++ b/src/tar.ts
@@ -35,14 +35,14 @@ async function getTarVersion(): Promise<TarVersion> {
   // Return whether this is GNU tar or BSD tar, and the version number
   if (stdout.includes("GNU tar")) {
     const match = stdout.match(/tar \(GNU tar\) ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
 
     return { type: "gnu", version: match[1] };
   } else if (stdout.includes("bsdtar")) {
     const match = stdout.match(/bsdtar ([0-9.]+)/);
-    if (!match || !match[1]) {
+    if (!match?.[1]) {
       throw new Error("Failed to parse output of tar --version.");
     }
 
diff --git a/src/workflow.ts b/src/workflow.ts
index ee95c337f5..adcb22baec 100644
--- a/src/workflow.ts
+++ b/src/workflow.ts
@@ -371,7 +371,7 @@ function getInputOrThrow(
       input = input.replace(`\${{matrix.${key}}}`, value);
     }
   }
-  if (input !== undefined && input.includes("${{")) {
+  if (input?.includes("${{")) {
     throw new Error(
       `Could not get ${inputName} input to ${actionName} since it contained an unrecognized dynamic value.`,
     );