Resteasy Reactive - Avoid NPE when using runtime converters

The NPE happens here: https://github.com/quarkusio/quarkus/blob/e6ffbe43243f9c852c61aafc307515be0915c6c8/extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/main/java/io/quarkus/resteasy/reactive/server/deployment/ClassInjectorTransformer.java#L222.

However, it's expected that the delegated converter is null when there are runtime converts. See related lines: https://github.com/quarkusio/quarkus/blob/bd87966540990fa68ec3769e22e67df1854b08a5/extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/main/java/io/quarkus/resteasy/reactive/server/deployment/QuarkusServerEndpointIndexer.java#L169 and https://github.com/quarkusio/quarkus/blob/bd87966540990fa68ec3769e22e67df1854b08a5/extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/main/java/io/quarkus/resteasy/reactive/server/deployment/QuarkusServerEndpointIndexer.java#L173.

Therefore, as It's possible that the delegate is null when there are runtime converters, we check whether the delegate is null and if it is, we don't use it to avoid the NPE. The rest works as expected as proven in the test.

Fixes quarkusio#21664

extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/main/java/io/quarkus/resteasy/reactive/server/deployment/ClassInjectorTransformer.java

@@ -296,7 +296,10 @@ private void generateConverterInitMethod(FieldInfo fieldInfo, ParameterConverter
 
         private ParameterConverterSupplier removeRuntimeResolvedConverterDelegate(ParameterConverterSupplier converter) {
             if (converter instanceof RuntimeResolvedConverter.Supplier) {
-                return ((RuntimeResolvedConverter.Supplier) converter).getDelegate();
+                ParameterConverterSupplier delegate = ((RuntimeResolvedConverter.Supplier) converter).getDelegate();
+                if (delegate != null) {
+                    return delegate;
+                }
             }
             return converter;
         }

extensions/resteasy-reactive/quarkus-resteasy-reactive/deployment/src/test/java/io/quarkus/resteasy/reactive/server/test/beanparam/CustomConverterInBeanParamTest.java

@@ -0,0 +1,98 @@
+package io.quarkus.resteasy.reactive.server.test.beanparam;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Type;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+import javax.ws.rs.BeanParam;
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.QueryParam;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.ext.ParamConverter;
+import javax.ws.rs.ext.ParamConverterProvider;
+import javax.ws.rs.ext.Provider;
+
+import org.jboss.shrinkwrap.api.ShrinkWrap;
+import org.jboss.shrinkwrap.api.spec.JavaArchive;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import io.quarkus.test.QuarkusUnitTest;
+import io.restassured.RestAssured;
+
+public class CustomConverterInBeanParamTest {
+
+    @RegisterExtension
+    static QuarkusUnitTest test = new QuarkusUnitTest()
+            .setArchiveProducer(() -> ShrinkWrap.create(JavaArchive.class)
+                    .addClasses(SearchResource.class, FilterData.class,
+                            JavaTimeParamConverterProvider.class, LocalDateTimeParamConverter.class));
+
+    @Test
+    void shouldCustomConvertBeUsedForLocalDateTimeInFilterData() {
+        LocalDateTime since = LocalDateTime.now();
+        String request = since.format(DateTimeFormatter.ISO_DATE_TIME);
+        String expected = since.plusYears(1).format(DateTimeFormatter.ISO_DATE_TIME);
+
+        RestAssured.get("/search?since=" + request)
+                .then()
+                .statusCode(200)
+                .body(equalTo("Got: " + expected));
+    }
+
+    @Path("/search")
+    public static class SearchResource {
+
+        @GET
+        @Produces(MediaType.TEXT_PLAIN)
+        public String search(@BeanParam FilterData filter) {
+            return "Got: " + filter.getSince().plusYears(1).format(DateTimeFormatter.ISO_DATE_TIME);
+        }
+    }
+
+    public static class FilterData {
+
+        @QueryParam("since")
+        private LocalDateTime since;
+
+        public LocalDateTime getSince() {
+            return since;
+        }
+
+        public void setSince(LocalDateTime since) {
+            this.since = since;
+        }
+    }
+
+    public static class LocalDateTimeParamConverter implements ParamConverter<LocalDateTime> {
+
+        @Override
+        public LocalDateTime fromString(String value) {
+            return LocalDateTime.parse(value, DateTimeFormatter.ISO_DATE_TIME);
+        }
+
+        @Override
+        public String toString(LocalDateTime value) {
+            return value.format(DateTimeFormatter.ISO_DATE_TIME);
+        }
+    }
+
+    @Provider
+    public static class JavaTimeParamConverterProvider implements ParamConverterProvider {
+
+        @Override
+        public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {
+            if (rawType == LocalDateTime.class) {
+                return (ParamConverter<T>) new LocalDateTimeParamConverter();
+            }
+
+            return null;
+        }
+
+    }
+}