Anuken/Mindustry · error · IllegalArgumentException

Unit stances must be strings.

Error message

Unit stances must be strings.

What it means

Thrown by the UnitStance parser when data is not a string. Stances resolve only by name, so object/number/array values are rejected before any lookup.

Source

Thrown at core/src/mindustry/mod/ContentParser.java:176

               if(cmd != null){
                   return cmd;
               }else{
                   throw new IllegalArgumentException("Unknown unit command name: " + data.asString());
               }
            }else{
                throw new IllegalArgumentException("Unit commands must be strings.");
            }
        });
        put(UnitStance.class, (type, data) -> {
            if(data.isString()){
                var cmd = content.unitStance(data.asString());
                if(cmd != null){
                    return cmd;
                }else{
                    throw new IllegalArgumentException("Unknown unit stance name: " + data.asString());
                }
            }else{
                throw new IllegalArgumentException("Unit stances must be strings.");
            }
        });
        put(BulletType.class, (type, data) -> {
            if(data.isString()){
                return field(Bullets.class, data);
            }else if(data.isArray()){
                return new MultiBulletType(parser.readValue(BulletType[].class, data));
            }
            Class<?> alternate = resolve(Strings.capitalize(data.getString("type", "basic")) + "BulletType", Object.class, false);
            Class<?> bc = alternate == Object.class ? resolve(data.getString("type", ""), BasicBulletType.class) : alternate;
            data.remove("type");
            BulletType result = (BulletType)make(bc);
            result.minfo.mod = currentMod;
            readFields(result, data);
            return result;
        });
        put(MassDriverBolt.class, (type, data) -> {
            MassDriverBolt result = make(MassDriverBolt.class);

View on GitHub (pinned to f695ad7e60)

Solutions

1. Provide the stance as a quoted string.
2. Use a registered stance name.

Example fix

// before
"stance": { "name": "stop" }
// after
"stance": "stop"

// Guard: unit stance value must be a JSON string.
boolean isStanceRef(JsonValue v) { return v.isString(); }

When it happens

Trigger: A mod JSON supplies a unit stance field as a non-string JSON value.

Common situations: Missing quotes around the stance name, or attempting object-style configuration not supported for stances.

Related errors

• Unknown unit stance name:
• Attribute definitions must be objects, e.g. {heat: 10}
• Unknown status effect: '
• Unknown unit command name:
• Unit commands must be strings.

AI-assisted analysis of Anuken/Mindustry@f695ad7e60 (2026-08-14). Data as JSON: /api/errors/7de636f6669f28ae. Report an issue: GitHub.