Demo application to demonstrate an issue using the spring-javaformat checkstyle rules with switch expressions.

→ spring-io/spring-javaformat#300

Issue

The default spring-javaformat checkstyle rules includes the SpringLambdaCheck which throws the following exception if the source code contains a switch expression.

Example source code

String message = switch (args.length) {
case 0 -> "No arg";
case 1 -> "One arg";
default -> getText.apply(args.length);
};

A full code example could be found in this repository:

• POM: pom.xml
• Checkstyle config: checkstyle.xml
• Example Java class: SampleApplication.java

Exception

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.1.2:check (default-cli) on project spring-javaformat-maven-sample: Failed during checkstyle configuration: Exception was thrown while processing /home/reichardt/Projects/_github/SpringLambdaCheck-with-switch-expression/src/main/java/sample/SampleApplication.java: Cannot invoke "com.puppycrawl.tools.checkstyle.api.DetailAST.getChildCount(int)" because "ast" is null -> [Help 1]

How to reproduce

1. Clone this repo
2. Run mvn checkstyle:check
   → The error occurs

Workaround

Exclude the SpringLambdaCheck, see comment in checkstyle.xml.