[SUREFIRE-1735] Using GraalVM toolchain causes NPE when default JAVA_HOME is not set to GraalVM JDK's home

**[Adam Czepil](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=kopper)** opened **[SUREFIRE-1735](https://issues.apache.org/jira/browse/SUREFIRE-1735?redirect=false)** and commented

When I use toolchains and configure GraalVM as the active toolchain AND my default JDK is NOT GraalVM (JAVA_HOME != GraalVM) I'm getting NPE from surefire plugin

**Caused by**: java.lang.NullPointerException

    **at** org.apache.maven.surefire.booter.SystemUtils.toJdkVersionFromReleaseFile (**SystemUtils.java:141**)

    **at** org.apache.maven.surefire.booter.SystemUtils.isJava9AtLeast (**SystemUtils.java:215**)

    **at** org.apache.maven.plugin.surefire.AbstractSurefireMojo.getEffectiveJvm (**AbstractSurefireMojo.java:2446**)

It works fine when I change JAVA_HOME to point to GraalVM home.

The reason is that https://github.com/apache/maven-surefire/blob/master/surefire-booter/src/main/java/org/apache/maven/surefire/booter/SystemUtils.java try to read JAVA_VERSION from releases file and GraalVM doesn't have this variable there.

I'm not sure who is at fault, maybe GraalVM should export that var.

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**Affects:** 3.0.0-M4

Start in surefire-booter/src/main/java/org/apache/maven/surefire/booter/SystemUtils.java, especially toJdkVersionFromReleaseFile and isJava9AtLeast at the reported lines. Reproduce the toolchain setup with GraalVM selected while JAVA_HOME points elsewhere, then verify that Surefire no longer throws the reported NullPointerException and still determines the effective JVM correctly.

Written by the indexing model from the issue text.