Regression: Null pointer exception when enabling continuous testing

[Sgitario]

Describe the bug

This issue is caused by this commit: 8d49f1e

Basically, doing mvn quarkus:dev and pressing the key r (resuming testing), we will get the exception:

__  ____  __  _____   ___  __ ____  ______ 
 --/ __ \/ / / / _ | / _ \/ //_/ / / / __/ 
 -/ /_/ / /_/ / __ |/ , _/ ,< / /_/ /\ \   
--\___\_\____/_/ |_/_/|_/_/|_|\____/___/   
2021-07-29 13:51:26,833 INFO  [io.quarkus] (Quarkus Main Thread) examples-greetings 0.0.4-SNAPSHOT on JVM (powered by Quarkus 999-SNAPSHOT) started in 1.565s. Listening on: http://localhost:8080
2021-07-29 13:51:26,837 INFO  [io.quarkus] (Quarkus Main Thread) Profile dev activated. Live Coding activated.
2021-07-29 13:51:26,838 INFO  [io.quarkus] (Quarkus Main Thread) Installed features: [cdi, resteasy, smallrye-context-propagation]
2021-07-29 13:51:31,041 ERROR [io.qua.dep.dev.tes.TestSupport] (Aesh InputStream Reader) Failed to create compiler, runtime compilation will be unavailable: java.lang.NullPointerException
	at io.quarkus.deployment.dev.RuntimeUpdatesProcessor.startTestScanningTimer(RuntimeUpdatesProcessor.java:268)
	at io.quarkus.deployment.dev.RuntimeUpdatesProcessor.checkForChangedTestClasses(RuntimeUpdatesProcessor.java:605)
	at io.quarkus.deployment.dev.RuntimeUpdatesProcessor$1.testsEnabled(RuntimeUpdatesProcessor.java:147)
	at io.quarkus.deployment.dev.testing.TestSupport.start(TestSupport.java:106)
	at io.quarkus.deployment.dev.testing.TestConsoleHandler$2.run(TestConsoleHandler.java:94)
	at io.quarkus.deployment.console.ConsoleStateManager$1.accept(ConsoleStateManager.java:73)
	at io.quarkus.deployment.console.ConsoleStateManager$1.accept(ConsoleStateManager.java:46)
	at io.quarkus.deployment.console.AeshConsole.lambda$setup$1(AeshConsole.java:199)
	at org.aesh.terminal.EventDecoder.accept(EventDecoder.java:118)
	at org.aesh.terminal.EventDecoder.accept(EventDecoder.java:31)
	at org.aesh.terminal.io.Decoder.write(Decoder.java:133)
	at org.aesh.readline.tty.terminal.TerminalConnection.openBlocking(TerminalConnection.java:216)
	at org.aesh.readline.tty.terminal.TerminalConnection.openBlocking(TerminalConnection.java:203)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)

Other consequences (not sure if related to the null pointer or not) are that when adding a new test, this test is indeed detected and executed, but it never ends:

Running 1/1. Running: io.quarkus.qe.GreetingResourceTest#shouldSayVictor()

Expected behavior

No response

Actual behavior

No response

How to Reproduce?

No response

Output of uname -a or ver

No response

Output of java -version

No response

GraalVM version (if different from Java)

No response

Quarkus version or git rev

No response

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

No response

Additional information

No response

[quarkus-bot]

/cc @stuartwdouglas

[geoand]

I assume it's as simple as #19093