diff --git a/dev-infra/commit-message/validate-file/cli.ts b/dev-infra/commit-message/validate-file/cli.ts
index 82f9800c3e93e..8ba2d5b2856b3 100644
--- a/dev-infra/commit-message/validate-file/cli.ts
+++ b/dev-infra/commit-message/validate-file/cli.ts
@@ -31,7 +31,10 @@ function builder(yargs: Argv) {
         type: 'string',
         conflicts: ['file'],
         description: 'The key of the environment variable for the path of the commit message file.',
-        coerce: (arg: string) => {
+        coerce: (arg: string|undefined) => {
+          if (arg === undefined) {
+            return arg;
+          }
           const file = process.env[arg];
           if (!file) {
             throw new Error(`Provided environment variable "${arg}" was not found.`);
diff --git a/dev-infra/ng-dev.js b/dev-infra/ng-dev.js
index 4b32b869bd67f..092428181995d 100755
--- a/dev-infra/ng-dev.js
+++ b/dev-infra/ng-dev.js
@@ -2101,6 +2101,9 @@ function builder$2(yargs) {
         conflicts: ['file'],
         description: 'The key of the environment variable for the path of the commit message file.',
         coerce: (arg) => {
+            if (arg === undefined) {
+                return arg;
+            }
             const file = process.env[arg];
             if (!file) {
                 throw new Error(`Provided environment variable "${arg}" was not found.`);