[REQ] [Kotlin] Default optional parameters to null
Author: rupert-jung-mwCreated Sep 17, 2026Updated Sep 17, 2026
LabelsEnhancement: Feature
Is your feature request related to a problem? Please describe.
While non-required properties of generatered DTOs are defaulted to null this is not true to non-required parameters.
Example:
Describe the solution you'd like
= null added to optional parameters
Additional context
Generator: kotlin-server Library: jaxrs-spec
Options:
<configOptions>
<library>jaxrs-spec</library>
<!-- Required for Quarkus 3.x (Jakarta EE 10): uses jakarta.* instead of javax.* imports -->
<useJakartaEe>true</useJakartaEe>
<useSwaggerAnnotations>false</useSwaggerAnnotations>
<sourceFolder>src/main/java</sourceFolder>
<dateLibrary>java8</dateLibrary>
<serializationLibrary>jackson</serializationLibrary>
<useBeanValidation>true</useBeanValidation>
<openApiNullable>false</openApiNullable>
<sortModelPropertiesByRequiredFlag>true</sortModelPropertiesByRequiredFlag>
<sortParamsByRequiredFlag>true</sortParamsByRequiredFlag>
<interfaceOnly>true</interfaceOnly>
</configOptions>I got it to work by adding a custom Mustache template querParams.mustache to my template directory:
{{#isQueryParam}}@QueryParam("{{#lambda.escapeDollar}}{{baseName}}{{/lambda.escapeDollar}}"){{#useBeanValidation}}{{>beanValidationQueryParams}}{{/useBeanValidation}}{{^isContainer}}{{#defaultValue}} @DefaultValue({{#lambda.doublequote}}{{{.}}}{{/lambda.doublequote}}){{/defaultValue}}{{/isContainer}} {{paramName}}: {{{dataType}}}{{#isNullable}}?{{/isNullable}}{{^isNullable}}{{^defaultValue}}{{^required}}? = null{{/required}}{{/defaultValue}}{{/isNullable}}{{/isQueryParam}}(Code above has been generated by Claude Sonnet 5)
Maybe this could be validated by some experienced dev and included in one of the next releases :)
Thank you!
Source: OpenAPITools/openapi-generator