Get latest mandrel release if version not specified

Update doc.

.github/workflows/test.yml

@@ -199,6 +199,10 @@ jobs:
             java-version: '17'
             distribution: '' # test empty distribution for backward compatibility
             os: ubuntu-latest
+          - version: '' # test with no version
+            java-version: '21'
+            distribution: 'mandrel'
+            os: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - name: Run setup-graalvm action

README.md

@@ -176,7 +176,7 @@ jobs:
 | `native-image-job-reports` *) | `'false'` | If set to `'true'`, post a job summary containing a Native Image build report. |
 | `native-image-pr-reports`  *) | `'false'` | If set to `'true'`, post a comment containing a Native Image build report on pull requests. Requires `write` permissions for the [`pull-requests` scope][gha-permissions]. |
 | `components`    | `''`     | Comma-separated list of GraalVM components (e.g., `native-image` or `ruby,nodejs`) that will be installed by the [GraalVM Updater][gu]. |
-| `version` | `''` | `X.Y.Z` (e.g., `22.3.0`) for a specific [GraalVM release][releases] up to `22.3.2`<br>`mandrel-X.Y.Z` (e.g., `mandrel-21.3.0.0-Final`) for a specific [Mandrel release][mandrel-releases],<br>`mandrel-latest` for [latest Mandrel stable release][mandrel-stable]. |
+| `version` | `''` | `X.Y.Z` (e.g., `22.3.0`) for a specific [GraalVM release][releases] up to `22.3.2`<br>`mandrel-X.Y.Z.W` or `X.Y.Z.W-Final` (e.g., `mandrel-21.3.0.0-Final` or `21.3.0.0-Final`) for a specific [Mandrel release][mandrel-releases],<br>`mandrel-latest` or `latest` for the latest Mandrel stable release. |
 | `gds-token`     | `''`     | Download token for the GraalVM Download Service. If a non-empty token is provided, the action will set up GraalVM Enterprise Edition (see [GraalVM EE template](#template-for-graalvm-enterprise-edition)). |
 
 **) Make sure that Native Image is used only once per build job. Otherwise, the report is only generated for the last Native Image build.*

src/mandrel.ts

@@ -21,6 +21,8 @@ export async function setUpMandrel(
   const version = stripMandrelNamespace(mandrelVersion)
   let mandrelHome
   switch (version) {
+    case '':
+    // fetch latest if no version is specified
     case 'latest':
       mandrelHome = await setUpMandrelLatest(javaVersion)
       break