diff --git a/dist/index.js b/dist/index.js
index c7b396f..d0c2fbf 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -13285,7 +13285,7 @@ const fs = __importStar(__nccwpck_require__(7147));
 const compare_versions_1 = __nccwpck_require__(4773); // compareVersions can be used in the sense of >
 // Don't throw on non-zero.
 const exec = async (cmd, args) => (0, exec_1.exec)(cmd, args, { ignoreReturnCode: true });
-function failed(tool, version) {
+async function failed(tool, version) {
     throw new Error(`All install methods for ${tool} ${version} failed`);
 }
 async function configureOutputs(tool, version, path, os) {
@@ -13731,7 +13731,7 @@ function parseYAMLBoolean(name, val) {
 exports.parseYAMLBoolean = parseYAMLBoolean;
 function parseURL(name, val) {
     if (val === '')
-        return undefined;
+        return null;
     try {
         return new URL(val);
     }
diff --git a/lib/installer.js b/lib/installer.js
index 798b54f..3902a03 100644
--- a/lib/installer.js
+++ b/lib/installer.js
@@ -40,7 +40,7 @@ const fs = __importStar(require("fs"));
 const compare_versions_1 = require("compare-versions"); // compareVersions can be used in the sense of >
 // Don't throw on non-zero.
 const exec = async (cmd, args) => (0, exec_1.exec)(cmd, args, { ignoreReturnCode: true });
-function failed(tool, version) {
+async function failed(tool, version) {
     throw new Error(`All install methods for ${tool} ${version} failed`);
 }
 async function configureOutputs(tool, version, path, os) {
diff --git a/src/installer.ts b/src/installer.ts
index 9d30f41..1b682fb 100644
--- a/src/installer.ts
+++ b/src/installer.ts
@@ -14,7 +14,7 @@ import {compareVersions} from 'compare-versions'; // compareVersions can be used
 const exec = async (cmd: string, args?: string[]): Promise<number> =>
   e(cmd, args, {ignoreReturnCode: true});
 
-function failed(tool: Tool, version: string): void {
+async function failed(tool: Tool, version: string): Promise<void> {
   throw new Error(`All install methods for ${tool} ${version} failed`);
 }
 
diff --git a/src/opts.ts b/src/opts.ts
index 9fe2dc1..7818af5 100644
--- a/src/opts.ts
+++ b/src/opts.ts
@@ -24,7 +24,7 @@ export interface ProgramOpt {
 
 export interface Options {
   ghc: ProgramOpt;
-  ghcup: {releaseChannel?: URL};
+  ghcup: {releaseChannel: URL | null};
   cabal: ProgramOpt & {update: boolean};
   stack: ProgramOpt & {setup: boolean};
   general: {matcher: {enable: boolean}};
@@ -138,8 +138,8 @@ export function parseYAMLBoolean(name: string, val: string): boolean {
   );
 }
 
-export function parseURL(name: string, val: string): URL | undefined {
-  if (val === '') return undefined;
+export function parseURL(name: string, val: string): URL | null {
+  if (val === '') return null;
   try {
     return new URL(val);
   } catch (e) {