[MNG-6170] NPE in cases using Multithreaded -T X versions:set -DnewVersion=1.0-SNAPSHOT

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1.1, 3.2.5, 3.3.1, 3.3.9
• Fix Version/s: 3.5.0-beta-1, 3.5.0
• Component/s: Core
• Assignee: Karl Heinz Marbaise
• Reporter: Karl Heinz Marbaise
• Created: 12/Feb/17 12:01
• Updated: 28/Mar/20 15:01
• Resolved: 12/Mar/17 14:44

Description

Based on the issue marked for the versions-maven-plugin investigation shows that the real cause of this problem is located in maven-core.

The short description of the problem is calling Maven via: mvn -T 20 versions:set -DnewVersion=1.0-SNAPSHOT you will get an NPE.

I identified the following point in code as culprit for the problem:

MultiThreadedBuilder.java

        // for each finished project
        for ( int i = 0; i < analyzer.getNumberOfBuilds(); i++ )
        {
            try
            {
                ProjectSegment projectBuild = service.take().get();
                if ( reactorContext.getReactorBuildStatus().isHalted() )
                {
                    break;
                }
                final List<MavenProject> newItemsThatCanBeBuilt =
                    analyzer.markAsFinished( projectBuild.getProject() );
                for ( MavenProject mavenProject : newItemsThatCanBeBuilt )
                {
                    ProjectSegment scheduledDependent = projectBuildList.get( mavenProject );
                    logger.debug( "Scheduling: " + scheduledDependent );
                    Callable<ProjectSegment> cb =
                        createBuildCallable( rootSession, scheduledDependent, reactorContext, taskSegment, muxer );
                    service.submit( cb );
                }
            }
            catch ( InterruptedException e )
            {
                rootSession.getResult().addException( e );
                break;
            }
            catch ( ExecutionException e )
            {
                // TODO MNG-5766 changes likely made this redundant 
                rootSession.getResult().addException( e );
                break;
            }
        }

And the problematic part is before the second debugging output line:

                    ProjectSegment scheduledDependent = projectBuildList.get( mavenProject );
                    logger.debug( "Scheduling: " + scheduledDependent );
                    Callable<ProjectSegment> cb =
                        createBuildCallable( rootSession, scheduledDependent, reactorContext, taskSegment, muxer );
                    service.submit( cb );

Cause it happens that the scheduledDependent could be null which will cause the issue.
This looks like is a regression, cause in Maven 3.0.5 it works without any issue.

Update:
I have found other examples where the NPE occurs:

• mvn -T20 javadoc:aggregate
• mvn -T20 install:install-file ...
  This can cause confusion if you are using mvn.config and put thing like -T X into it.