GWT : Class 'java.util.concurrent.CompletableFuture' is not present in JRE Emulation INTELLIJ IDEA

I am working on a GWT project in IntelliJ IDEA Ultimate 2023.3.2

All is running fine.

But IntelliJ keeps telling me that java class files are not present in JRE Emulation Library.

Please help :)

Class 'java.util.concurrent.CompletableFuture' is not present in JRE Emulation Library so it cannot be used in client code of 'com.srr.ShopManager' GWT module

Sorry did forget to add source is included from

<dependency>
    <groupId>com.ekotrope</groupId>
    <artifactId>gwt-completablefuture</artifactId>
    <version>1.0.0</version>
</dependency>

To fix this annoying error just open Settings -> Project Structure -> Facets. In the bottom right corner of popup you'll see a warning message that gwt-user jar are missing (or something else). Just click "Fix" and "Apply".

After this fix there are no error message about JRE emulation.

P.S. This link and this other link helped me.