OpenAPITools/openapi-generator · error · IllegalArgumentException

Invalid model property naming '{naming}'. Must be 'original'

Error message

Invalid model property naming '{naming}'. Must be 'original', 'camelCase', 'PascalCase' or 'snake_case'

What it means

AbstractScalaCodegen.setModelPropertyNaming calls CodegenConstants.ENUM_PROPERTY_NAMING_TYPE.valueOf(naming). An unrecognized string makes valueOf throw IllegalArgumentException, rethrown with the allowed list 'original', 'camelCase', 'PascalCase', 'snake_case' — matched case-sensitively against the enum constant names.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractScalaCodegen.java:270

    public void setDateLibrary(String dateLibrary, boolean withLegacy) {
        if (withLegacy && dateLibrary.equals(DateLibraries.legacy.name())) {
            this.dateLibrary = dateLibrary;
            return;
        }
        for (DateLibraries dateLib : DateLibraries.values()) {
            if (dateLib.name().equals(dateLibrary)) {
                this.dateLibrary = dateLibrary;
                return;
            }
        }
        throw new IllegalArgumentException("Invalid dateLibrary. Must be 'java8' or 'joda'");
    }

    public void setModelPropertyNaming(String naming) {
        try {
            this.modelPropertyNaming = CodegenConstants.ENUM_PROPERTY_NAMING_TYPE.valueOf(naming).name();
        } catch (IllegalArgumentException ex) {
            throw new IllegalArgumentException("Invalid model property naming '" +
                    naming + "'. Must be 'original', 'camelCase', " +
                    "'PascalCase' or 'snake_case'");
        }
    }


    @Override
    public String toVarName(String name) {
        // obtain the name from nameMapping directly if provided
        if (nameMapping.containsKey(name)) {
            return nameMapping.get(name);
        }

        String varName = sanitizeName(name);

        if ("_".equals(varName)) {
            varName = "_u";
        }

View on GitHub (pinned to fcec517be3)

Solutions

Pass one of the exact values: original, camelCase, PascalCase, snake_case
For underscore naming write it fully: -p modelPropertyNaming=snake_case
Omit the option to keep the generator default while you check the README table

Example fix

# before
-p modelPropertyNaming=snake

# after
-p modelPropertyNaming=snake_case

Defensive patterns

Strategy: validation

Validate before calling

// Java: validate against the enum before applying
try {
    CodegenConstants.ENUM_PROPERTY_NAMING_TYPE.valueOf(naming);
} catch (IllegalArgumentException ex) {
    throw new IllegalArgumentException("modelPropertyNaming must be original, camelCase, PascalCase or snake_case");
}

Try / catch

try { generator.generate(); } catch (IllegalArgumentException e) { if (e.getMessage().contains("Invalid model property naming")) { /* fix the casing option value */ } throw e; }

Prevention

Copy option values from the generator's README table, exactly as printed
Treat naming values as case-sensitive enum names
Centralize generator options in a reviewed config file

When it happens

Trigger: -p modelPropertyNaming=<bad> on Scala generators: 'snake' (missing _case), 'Pascalcase' or 'pascalcase' (wrong case), 'kebab-case', 'hyphen', 'camel_case'.

Common situations: Muscle memory from other tools' naming options; assuming case-insensitive matching; copy-pasting values between generators whose option vocabularies differ.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/b961d78636234ec1. Report an issue: GitHub.