PackageJson: Disallow undefined in exports (#626)

source/package-json.d.ts

@@ -208,26 +208,12 @@ declare namespace PackageJson {
 	*/
 	export type Dependency = Partial<Record<string, string>>;
 
-	/**
-	Conditions which provide a way to resolve a package entry point based on the environment.
-	*/
-	export type ExportCondition = LiteralUnion<
-	| 'import'
-	| 'require'
-	| 'node'
-	| 'node-addons'
-	| 'deno'
-	| 'browser'
-	| 'electron'
-	| 'react-native'
-	| 'default',
-	string
-	>;
-
 	/**
 	A mapping of conditions and the paths to which they resolve.
 	*/
-	type ExportConditions = {[condition in ExportCondition]?: Exports};
+	type ExportConditions = { // eslint-disable-line @typescript-eslint/consistent-indexed-object-style
+		[condition: string]: Exports;
+	};
 
 	/**
 	Entry points of a module, optionally with conditions and subpath exports.

test-d/package-json.ts

@@ -70,6 +70,9 @@ expectAssignable<PackageJson.Exports>({
 		default: './horse.js',
 	},
 });
+expectNotAssignable<PackageJson.Exports>({
+	'./unicorn': undefined,
+});
 expectNotAssignable<PackageJson.Imports>({unicorn: 'unicorn'});
 expectType<boolean | undefined>(packageJson.preferGlobal);
 expectType<boolean | undefined>(packageJson.private);