[BUG][JAVA] Multi-module spring-boot app gives errors about ApplicationContext and "multiple SLF4J bindings" warning

Description:

TL;DR.
I made a simple multi-module maven spring-boot app but building this fails with an error: Failed to load ApplicationContext
caused by: LoggerFactory is not a Logback LoggerContext but Logback is on the classpath. ....

Details:
I have made a spring boot app with 2 modules that build correclty.
Adding the dependency of org.openapitools:openapi-generator:5.4.0 results in an error: Failed to load ApplicationContext (for the test unit) and was apparently caused by LoggerFactory is not a Logback LoggerContext but Logback is on the classpath. ....

A few lines above this error I have this warning:
SLF4J: Class path contains multiple SLF4J bindings.

Note that the addition of the dependency was enough for the exception to occur. No generation has been done!

I think the addition of this dependency should not result in an error in the app, especially because it seems related to the logging framework.

Facts

org.openapitools:openapi-generator:5.4.0
spring-boot application: 2.6.7 (from initializr converted to multi-module)

Code

5 Project files and a directory tree

• Tree.txt: shows the directory structure
• \pom.xml
• \OpenApi\pom.xml
• \server\pom.xml
• \server\src\main\java\com\example\demo\DemoApplication.java
• \server\src\test\java\com\example\demo\DemoApplicationTests.java

Workaround
I was able to workaround the issue by excluding the slf4j-simple artifact from the generator (see also commented code in OpenApi\pom.xml):

Start with the linked root, OpenApi, and server pom.xml files, then inspect server/src/test/java/com/example/demo/DemoApplicationTests.java. Run the test with org.openapitools:openapi-generator:5.4.0 present and compare it with the slf4j-simple exclusion workaround. Done means the multi-module Spring Boot test runs without the ApplicationContext failure or multiple-binding warning.