07:49:50,752 ERROR [org.jboss.resteasy.core.providerfactory.DefaultExceptionMapper] (XNIO-1 task-3) RESTEASY002375: Error processing request POST /test/multi-injected - org.jboss.resteasy.plugins.providers.multipart.MultipartEntityPartProviderTest$TestResource.multipleInjectable: java.lang.NullPointerException: Cannot invoke "io.undertow.servlet.spec.AsyncContextImpl.addAsyncTask(java.lang.Runnable)" because "this.asyncContext" is null
    at io.undertow.servlet.spec.ServletOutputStreamImpl.setWriteListener(ServletOutputStreamImpl.java:807)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletResponseWrapper$WrappedServletOutputStream.setWriteListener(HttpServletResponseWrapper.java:591)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletResponseWrapper$DeferredOutputStream.queue(HttpServletResponseWrapper.java:298)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletResponseWrapper$DeferredOutputStream.asyncWrite(HttpServletResponseWrapper.java:281)
    at org.jboss.resteasy.util.CommitHeaderAsyncOutputStream.asyncWrite(CommitHeaderAsyncOutputStream.java:80)
    at org.jboss.resteasy.spi.AsyncOutputStream.asyncWrite(AsyncOutputStream.java:25)
    at org.jboss.resteasy.plugins.providers.multipart.AbstractMultipartWriter.asyncWritePart(AbstractMultipartWriter.java:202)
    at org.jboss.resteasy.plugins.providers.multipart.AbstractMultipartFormDataWriter.lambda$asyncWriteParts$0(AbstractMultipartFormDataWriter.java:62)
    at java.base/java.util.concurrent.CompletableFuture.uniComposeStage(CompletableFuture.java:1187)
    at java.base/java.util.concurrent.CompletableFuture.thenCompose(CompletableFuture.java:2341)
    at java.base/java.util.concurrent.CompletableFuture.thenCompose(CompletableFuture.java:144)
    at org.jboss.resteasy.plugins.providers.multipart.AbstractMultipartFormDataWriter.asyncWriteParts(AbstractMultipartFormDataWriter.java:62)
    at org.jboss.resteasy.plugins.providers.multipart.AbstractMultipartWriter.asyncWrite(AbstractMultipartWriter.java:137)
    at org.jboss.resteasy.plugins.providers.multipart.MultipartEntityPartWriter.lambda$asyncWriteTo$1(MultipartEntityPartWriter.java:58)
    at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1150)
    at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
    at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1773)
    at org.jboss.resteasy.concurrent.ContextualExecutors.lambda$runnable$2(ContextualExecutors.java:312)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
    at java.base/java.lang.Thread.run(Thread.java:1583)

asyncContext = (AsyncContextImpl) servletRequest.getAsyncContext();
listener = writeListener;
//we register the write listener on the underlying connection
//so we don't have to force the creation of the response channel
//under normal circumstances this will break write listener delegation
this.internalListener = new WriteChannelListener();
if (this.channel != null) {
    this.channel.getWriteSetter().set(internalListener);
}
//we resume from an async task, after the request has been dispatched
asyncContext.addAsyncTask(new Runnable() {
    @Override
    public void run() {
        asyncIoStarted = true;
        if (channel == null) {
            servletRequestContext.getExchange().getIoThread().execute(new Runnable() {
                @Override
                public void run() {
                    internalListener.handleEvent(null);
                }
            });
        } else {
            channel.resumeWrites();
        }
    }
});