Building a Maven project with Spring Boot 2.3.0.BUILD-SNAPSHOT as the parent leads to:

[INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ test-netty ---
[WARNING] File encoding has not been set, using platform encoding US-ASCII, i.e. build is platform dependent!
[WARNING] Please take a look into the FAQ: https://maven.apache.org/general.html#encoding-warning
[WARNING] Using platform encoding (US-ASCII actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 1 resource
[INFO] Copying 0 resource
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.1:compile (default-compile) @ test-netty ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding US-ASCII, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /Users/snicoll/workspace/temp/test-netty/target/classes
[INFO] 
[INFO] --- maven-resources-plugin:3.1.0:testResources (default-testResources) @ test-netty ---
[WARNING] Using platform encoding (US-ASCII actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/snicoll/workspace/temp/test-netty/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ test-netty ---
[INFO] Changes detected - recompiling the module!
[WARNING] File encoding has not been set, using platform encoding US-ASCII, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /Users/snicoll/workspace/temp/test-netty/target/test-classes
[INFO] 

Those warnings are due to the fact that the UTF-8 encoding is not longer available. spring-boot-starter-parent should have <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

Comment From: snicoll

Closing in favour of PR #19835