Utils: Fix getServerVersionFromPackageJson

The cache is never null, because it defaults to undefined, and therefore this function always returns undefined.

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/utils/serverVersion.spec.ts

@@ -0,0 +1,27 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { promises as fs } from 'fs';
+import { getServerVersionFromPackageJson } from './serverVersion';
+
+it('getServerVersionFromPackageJson works', async () => {
+  const major = 2;
+  const minor = 0;
+  const patch = 0;
+  const preRelease = 'dev';
+  /* eslint-disable @typescript-eslint/require-await*/
+  jest.spyOn(fs, 'readFile').mockImplementationOnce(async (_) => {
+    return `{
+"version": "${major}.${minor}.${patch}"
+}
+`;
+  });
+  const serverVersion = await getServerVersionFromPackageJson();
+  expect(serverVersion.major).toEqual(major);
+  expect(serverVersion.minor).toEqual(minor);
+  expect(serverVersion.patch).toEqual(patch);
+  expect(serverVersion.preRelease).toEqual(preRelease);
+});

src/utils/serverVersion.ts

@@ -11,7 +11,7 @@ import { join as joinPath } from 'path';
 let versionCache: ServerVersion;
 
 export async function getServerVersionFromPackageJson(): Promise<ServerVersion> {
-  if (versionCache === null) {
+  if (versionCache === undefined) {
     const rawFileContent: string = await fs.readFile(
       joinPath(__dirname, '../../package.json'),
       { encoding: 'utf8' },