quarkus: Error in context propagation tutorial

Describe the bug Unexpected behaviour when I try to use code from Usage example for CompletionStage

Expected behavior Store persons to Postgre.

Actual behavior Compile exception. Need to change CompletionStage<Person> => CompletionStage<List<Person>>

Getting error: gist-link RESTEASY002020: Unhandled asynchronous exception, sending back 500: java.lang.IllegalStateException: You have attempted to perform a blocking operation on a IO thread. This is not allowed, as blocking the IO thread will cause major performance issues with your application. If you want to perform blocking EntityManager operations make sure you are doing it from a worker thread.

To Reproduce Steps to reproduce the behavior:

1. use code from tutorial
2. mvn clean quarkus:dev

Screenshots (If applicable, add screenshots to help explain your problem.)

Environment (please complete the following information):

• Output of uname -a or ver: Darwin MacBook-Pro-Sergey.local 18.7.0 Darwin Kernel Version 18.7.0: Sun Dec 1 18:59:03 PST 2019; root:xnu-4903.278.19~1/RELEASE_X86_64 x86_64
• Output of java -version: OpenJDK Runtime Environment GraalVM CE 19.3.1 (build 11.0.6+9-jvmci-19.3-b07) OpenJDK 64-Bit Server VM GraalVM CE 19.3.1 (build 11.0.6+9-jvmci-19.3-b07, mixed mode, sharing)
• GraalVM version (if different from Java): GraalVM CE 19.3.1
• Quarkus version or git rev: 1.2.0.Final