Jersey Microprofile RestClient - NullPointerException when a optional FormParam is null

[wagonli]

Currently using Jersey 2.35 (does not seem fixed in current release 3.1.1) we're encountering an unexpected behavior while using Jersey's Microprofile RestClient implementation. We're trying to issue requests to an enpoint accepting nullable application/x-www-form-urlencoded parameters and we're getting a NullPointerException each time we're trying to pass a null (@FormParam) parameter.

The issue seems to be caused by org.glassfish.jersey.microprofile.restclient.FormParamModel class that resolve the parameter value as Object and tries to call resolvedValue.toString() without a null-check.

jersey/ext/microprofile/mp-rest-client/src/main/java/org/glassfish/jersey/microprofile/restclient/FormParamModel.java

Line 48 in dc51308

form.param(formParamName, resolvedValue.toString());

Here is our setup :

Given the following resource :

@Path("/resource")
public interface MyResource {
    @POST
    @Consumes(APPLICATION_FORM_URLENCODED)
    @Produces(APPLICATION_JSON)
    void endpoint(
            @FormParam("param")
            String param
    );

The resulting client throws an exception when called with null value for param :

RestClientBuilder.newBuilder()
                               .register(JACKSON_CONTEXT_RESOLVER)
                               .register(JACKSON_JSON_PROVIDER, MessageBodyReader.class, MessageBodyWriter.class)
                               .baseUri(URI.create(MY8SERVICE_URL))
                               .build(MyResource.class)
                               .endpoint(null);

Resulting exception :
java.lang.RuntimeException: java.lang.NullPointerException: Cannot invoke "Object.toString()" because "resolvedValue" is null

Caused by: java.lang.NullPointerException: Cannot invoke "Object.toString()" because "resolvedValue" is null
	at org.glassfish.jersey.microprofile.restclient.FormParamModel.handleParameter(FormParamModel.java:48)
	at org.glassfish.jersey.microprofile.restclient.FormParamModel.handleParameter(FormParamModel.java:31)
	at org.glassfish.jersey.microprofile.restclient.MethodModel.lambda$handleForm$4(MethodModel.java:213)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
	at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:596)
	at org.glassfish.jersey.microprofile.restclient.MethodModel.handleForm(MethodModel.java:213)
	at org.glassfish.jersey.microprofile.restclient.MethodModel.invokeMethod(MethodModel.java:172)
	at org.glassfish.jersey.microprofile.restclient.InterceptorInvocationContext.proceed(InterceptorInvocationContext.java:110)
	at org.glassfish.jersey.microprofile.restclient.RestClientModel.invokeMethod(RestClientModel.java:69)
	at org.glassfish.jersey.microprofile.restclient.ProxyInvocationHandler.invoke(ProxyInvocationHandler.java:70)
	...

[wagonli]

Issue has been fixed