Exactly same issue I'm facing with Drools 8 or Drools 10.1.0. [Drools 10.1.0]

Everything works fine in Intellij. If deploy it to Linux (RHEL 7.0) getting NPE.

Caused by: java.lang.NullPointerException: Cannot invoke "org.kie.api.KieServices.newKieFileSystem()" because "this.ks" is null
        at org.kie.internal.utils.KieHelper.<init>(KieHelper.java:52)

Added META-INF as below:

kie.conf content:

# KIE configuration file for Drools
# Example: Specify the KieServices implementation
org.kie.api.KieServices = org.drools.compiler.kie.builder.impl.KieServicesImpl
org.kie.internal.builder.KnowledgeBuilderFactoryService = org.drools.compiler.builder.impl.KnowledgeBuilderFactoryServiceImpl

Simple Code:

public static StatelessKieSession buildStatelessKieSession(List<String> drlFiles) {
    KieHelper kieHelper = new KieHelper();
    for(String drlFile : drlFiles){
        kieHelper.addContent(drlFile, ResourceType.DRL);
    }
    return kieHelper.build().newStatelessKieSession();
}