HMCL-dev/HMCL · error · JsonParseException

Curse Forge modpack manifest Mod loader id cannot be blank.

Error message

Curse Forge modpack manifest Mod loader id cannot be blank.

What it means

Validation of a modLoaders entry in a CurseForge manifest: the loader's 'id' must be non-blank. A missing id means HMCL cannot determine which mod loader (forge/fabric) the pack uses, so the manifest is rejected.

Solutions

1. Provide a valid loader id such as "forge-47.2.0" or "fabric-0.15.0" in each modLoaders entry
2. Re-export the manifest from the CurseForge app
3. Check the JSON uses the `id` key expected by the deserializer

Example fix

// before
{"minecraft":{"modLoaders":[{"id":"","primary":true}]}}
// after
{"minecraft":{"modLoaders":[{"id":"forge-47.2.0","primary":true}]}}

for (CurseManifestModLoader ml : manifest.getMinecraft().getModLoaders()) { if (isBlank(ml.getId())) throw new IllegalArgumentException("modLoader id blank"); }

boolean hasLoaderId(CurseManifestModLoader ml) { return ml != null && ml.getId() != null && !ml.getId().isBlank(); }

try { modLoader.validate(); } catch (JsonParseException e) { log.error("Manifest mod loader blank", e); }

When it happens

Trigger: Parsing a curse manifest whose minecraft.modLoaders[] entry has an empty/whitespace `id`, then calling validate().

Common situations: Manually written manifest with an unfilled modLoaders entry, export tool bug, or JSON key mismatch ("name" instead of "id") leaving id null.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• Instance
• Missing Project ID or File ID.
• CurseForge Manifest.gameVersion cannot be blank.
• Invalid library path:
• /assets/

AI-assisted analysis of HMCL-dev/HMCL@24702dc5a0 (2026-09-10). Data as JSON: /api/errors/33c58c2177bdc355. Report an issue: GitHub.

Appendix: source

Thrown at HMCLCore/src/main/java/org/jackhuang/hmcl/modpack/curse/CurseManifestModLoader.java:40

@Override
public void validate() throws JsonParseException {
    if (StringUtils.isBlank(id))
        throw new JsonParseException("Curse Forge modpack manifest Mod loader id cannot be blank.");
}

View on GitHub (pinned to 24702dc5a0)