Update version following semver with groovy in Jenkinsfile - jenkins

Question

I'm currently trying to automate the versioning of my maven project with a Jenkins (version 2.190.3) job and following the SemVer. So I have my Jenkinsfile and I'm doing something like that:
script {
def version = "1.2.4"
def pattern = ~/(\d{1,3})\.(\d{1,3})\.\d{1,4}$/
def newVersion = version.replaceFirst(pattern) { _,major,minor -> "${major}.${(minor as int) + 1}.0"}
}
The expectation is to have 1.3.0 in newVersion.
The code seems OK, working on web console but when I'm using Jenkins I have the following error:
java.lang.NullPointerException: Cannot execute null+1
Am I doing something wrong ?

Answer 1

Almost the exact answer to your question is given in this post: Jenkins groovy regex match string : Error: java.io.NotSerializableException: java.util.regex.Matcher
What it comes down to is that the script executed by Jenkins is kind of groovy, but not exactly executed as it is. It is transformed first to a serializable state (can be suspended, saved to file, transported, restored, resumed).
This doesn't work with certain objects that have state, but aren't serializable, including java.util.regex.Matcher, which is working under the hood of your regular expression. If you put this code in a method marked #NonCPS, the code is not transformed, and (more of less) executed as plain groovy.
#NonCPS
def foo() {
def version = "1.2.4"
def pattern = ~/(\d{1,3})\.(\d{1,3})\.\d{1,4}$/
def newVersion = version.replaceFirst(pattern) { _,major,minor -> "${major}.${(minor as int) + 1}.0"}
println "Version ${version} -> new ${newVersion}"
}
script {
foo()
}