Repository: quarkusio/quarkus
Issue: NullPointerException in Resteasy Reactive Client due to no Configuration

### Describe the bug

When using classic jaxrs ClientBuilder with implementation from Resteasy Reactive Client jars, the configuration is not initialized.

### Expected behavior

ClientRequestFilter(s) successfully registered with classic ClientBuilder

### Actual behavior

NullPointerException thrown from ```org.jboss.resteasy.reactive.client.impl.ClientBuilderImpl, line 313```


### How to Reproduce?

With dependencies:

```xml
io.quarkus.resteasy.reactive:resteasy-reactive-common:jar:2.7.1.Final
org.jboss.spec.javax.ws.rs:jboss-jaxrs-api_2.1_spec:jar:2.0.1.Final
```

Use the following code:

```java

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.ClientRequestFilter;

public static void main(String args[]) {
    ClientBuilder clientBuilder = ClientBuilder.newBuilder();
    for (ClientRequestFilter filter : filters) {
      // following line has NPE
      clientBuilder.register(filter);
    }
}
```

### Output of `uname -a` or `ver`

Darwin C02YD0B0JG5J.corp.proofpoint.com 20.6.0 Darwin Kernel Version 20.6.0: Wed Jan 12 22:22:42 PST 2022; root:xnu-7195.141.19~2/RELEASE_X86_64 x86_64

### Output of `java -version`

openjdk version "11.0.12" 2021-07-20

### GraalVM version (if different from Java)

_No response_

### Quarkus version or git rev

2.7.1.Final

### Build tool (ie. output of `mvnw --version` or `gradlew --version`)

Apache Maven 3.8.4 (9b656c72d54e5bacbed989b64718c159fe39b537)

### Additional information

_No response_

Changed files:
independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/test/java/io/quarkus/jaxrs/client/reactive/deployment/test/AsyncRestClientFilterTestCase.java

diff --git a/extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/test/java/io/quarkus/jaxrs/client/reactive/deployment/test/AsyncRestClientFilterTestCase.java b/extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/test/java/io/quarkus/jaxrs/client/reactive/deployment/test/AsyncRestClientFilterTestCase.java
index a8baa6b800d..d4389344a49 100644
--- a/extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/test/java/io/quarkus/jaxrs/client/reactive/deployment/test/AsyncRestClientFilterTestCase.java
+++ b/extensions/resteasy-reactive/jaxrs-client-reactive/deployment/src/test/java/io/quarkus/jaxrs/client/reactive/deployment/test/AsyncRestClientFilterTestCase.java
@@ -47,8 +47,10 @@ public class AsyncRestClientFilterTestCase {
 
     @BeforeEach
     public void before() {
-        client = ClientBuilder.newClient()
+        // register one filter with builder to test configuration inheritance
+        client = ClientBuilder.newBuilder()
                 .register(SyncClientRequestFilter.class)
+                .build()
                 .register(AsyncClientRequestFilter.class)
                 .register(AsyncClientResponseFilter.class);
     }
diff --git a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
index 6ca8e156ec7..b56f7b52b0d 100644
--- a/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
+++ b/independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/ClientBuilderImpl.java
@@ -20,6 +20,7 @@
 import java.util.regex.Pattern;
 import javax.net.ssl.HostnameVerifier;
 import javax.net.ssl.SSLContext;
+import javax.ws.rs.RuntimeType;
 import javax.ws.rs.client.ClientBuilder;
 import javax.ws.rs.core.Configuration;
 import org.jboss.logging.Logger;
@@ -62,6 +63,10 @@ public class ClientBuilderImpl extends ClientBuilder {
     private ClientLogger clientLogger = new DefaultClientLogger();
     private String userAgent = "Resteasy Reactive Client";
 
+    public ClientBuilderImpl() {
+        configuration = new ConfigurationImpl(RuntimeType.CLIENT);
+    }
+
     @Override
     public ClientBuilder withConfig(Configuration config) {
         this.configuration = new ConfigurationImpl(config);