REST Client Reactive: support null file in multipart

[michalszynkiewicz]

fixes #20606

[geoand]

LGTM

[geoand]

Does this fix a reported issue?

[quarkus-bot]

Failing Jobs - Building b5a8405

Status	Name	Step	Failures	Logs	Raw logs
✖	Gradle Tests - JDK 11 Windows	Build	Failures	Logs	Raw logs
✖	JVM Tests - JDK 11	Build	Failures	Logs	Raw logs
✖	JVM Tests - JDK 17	Build	Failures	Logs	Raw logs

Full information is available in the Build summary check run.

Failures

⚙️ Gradle Tests - JDK 11 Windows #

- Failing: integration-tests/gradle 

📦 integration-tests/gradle

✖ io.quarkus.gradle.devmode.QuarkusDevDependencyDevModeTest.main line 14 - More details - Source on GitHub

org.awaitility.core.ConditionTimeoutException: Condition with lambda expression in io.quarkus.test.devmode.util.DevModeTestUtils that uses java.util.function.Supplier, java.util.function.Supplierjava.util.concurrent.atomic.AtomicReference, java.util.concurrent.atomic.AtomicReferencejava.lang.String, java.lang.Stringboolean was not fulfilled within 1 minutes.
	at org.awaitility.core.ConditionAwaiter.await(ConditionAwaiter.java:166)
	at org.awaitility.core.CallableCondition.await(CallableCondition.java:78)

---

⚙️ JVM Tests - JDK 11 #

- Failing: integration-tests/oidc 

📦 integration-tests/oidc

✖ io.quarkus.it.keycloak.WebsocketOidcTestCase.websocketTest line 49 - More details - Source on GitHub

org.opentest4j.AssertionFailedError: expected: <hello [email protected]> but was: <null>
	at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
	at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)

---

⚙️ JVM Tests - JDK 17 #

- Failing: integration-tests/oidc 

📦 integration-tests/oidc

✖ io.quarkus.it.keycloak.WebsocketOidcTestCase.websocketTest line 49 - More details - Source on GitHub

org.opentest4j.AssertionFailedError: expected: <hello [email protected]> but was: <null>
	at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
	at org.junit.jupiter.api.AssertionUtils.failNotEqual(AssertionUtils.java:62)

[michalszynkiewicz]

It didn't when I created the PR but it has now, I linked it in the description