OpenAPITools/openapi-generator · error · IllegalArgumentException

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

Error message

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

What it means

Defensive default arm inside getNameUsingModelPropertyNaming of the k6 generator, which converts property names per the configured convention. The switch covers exactly the four MODEL_PROPERTY_NAMING_TYPE constants (original, camelCase, PascalCase, snake_case), making the default arm unreachable in practice — invalid values fail earlier in setModelPropertyNaming (K6ClientCodegen.java:853) or at valueOf(). The message also reports the property name being converted rather than the bad convention value, which is misleading.

Source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/K6ClientCodegen.java:768

        return reference.toString();
    }

    private String getTemplateVariable(String input) {
        return "${" + input + "}";
    }

    private String getNameUsingModelPropertyNaming(String name) {
        switch (CodegenConstants.MODEL_PROPERTY_NAMING_TYPE.valueOf(getModelPropertyNaming())) {
            case original:
                return name;
            case camelCase:
                return camelize(name, LOWERCASE_FIRST_LETTER);
            case PascalCase:
                return camelize(name);
            case snake_case:
                return underscore(name);
            default:
                throw new IllegalArgumentException("Invalid model property naming '" +
                        name + "'. Must be 'original', 'camelCase', " +
                        "'PascalCase' or 'snake_case'");
        }
    }

    @Override
    public String toVarName(String name) {
        // sanitize name
        name = sanitizeName(name);  // FIXME parameter should not be assigned. Also declare it as "final"

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

        // if it's all upper case, do nothing
        if (name.matches("^[A-Z_]*$")) {
            return name;
        }

View on GitHub (pinned to fcec517be3)

Solutions

Check the `modelPropertyNaming` option value — the setter at K6ClientCodegen.java:853 is the realistic throw site.
Use exactly original, camelCase, PascalCase, or snake_case.
In subclasses, always use the setter rather than assigning the field.

Example fix

# before
openapi-generator-cli generate -g k6 -i api.yaml -p modelPropertyNaming=camel_case
# after
openapi-generator-cli generate -g k6 -i api.yaml -p modelPropertyNaming=camelCase

Defensive patterns

Strategy: validation

Validate before calling

# validate the option; this branch is defensive, the setter at K6ClientCodegen:853 is the gate
mpn="${MODEL_PROPERTY_NAMING:-}"
[ -z "$mpn" ] || case "$mpn" in
  original|camelCase|PascalCase|snake_case) ;;
  *) echo "modelPropertyNaming must be original|camelCase|PascalCase|snake_case, got: $mpn" >&2; exit 2 ;;
esac

Type guard

private static final java.util.Set<String> NAMING_CONVENTIONS =
        java.util.Set.of("original", "camelCase", "PascalCase", "snake_case");

boolean isValidNamingConvention(String v) {
    return v != null && NAMING_CONVENTIONS.contains(v);
}

Try / catch

try {
    new DefaultGenerator().opts(clientOptInput).generate();
} catch (RuntimeException e) {
    failBuild("k6 naming config rejected: " + e.getMessage());
}

Prevention

Validate modelPropertyNaming against the four constants before generation.
Suspect the setter throw site when this wording appears.
Use the setter in subclasses; never assign the field.

When it happens

Trigger: Not reachable through supported inputs: `-p modelPropertyNaming=<bad>` is rejected by the setter first. Only direct field assignment in a subclass or a future enum constant without a case could trigger it.

Common situations: Essentially never fires; the same wording thrown from K6ClientCodegen.java:853 is what developers actually encounter.

Related errors

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/e7666035f13b3063. Report an issue: GitHub.