NullPointerException in MiniAccumuloClusterImpl.getProcesses()

[teamconfx]

Describe the bug
MiniAccumuloClusterImpl.getProcesses() throws NullPointerException when managerProcess is null due to missing null check, while other similar fields (zooKeeperProcess, gcProcess) have proper null checks.

Root Cause Analysis

The getProcesses() method has inconsistent null handling for process references:

public Map<ServerType,Collection<ProcessReference>> getProcesses() {
    Map<ServerType,Collection<ProcessReference>> result = new HashMap<>();
    MiniAccumuloClusterControl control = getClusterControl();
    result.put(ServerType.MANAGER, references(control.managerProcess));  // BUG: No null check!
    result.put(ServerType.TABLET_SERVER,
        references(control.tabletServerProcesses.toArray(new Process[0])));
    if (control.zooKeeperProcess != null) {  // Has null check
      result.put(ServerType.ZOOKEEPER, references(control.zooKeeperProcess));
    }
    if (control.gcProcess != null) {  // Has null check
      result.put(ServerType.GARBAGE_COLLECTOR, references(control.gcProcess));
    }
    return result;
}

When managerProcess is null (e.g., before cluster starts or after manager is stopped), it gets passed to references() which creates a ProcessReference:

List<ProcessReference> references(Process... procs) {
    return Stream.of(procs).map(ProcessReference::new).collect(toList());
}

The ProcessReference constructor enforces non-null:

ProcessReference(Process process) {
    this.process = Objects.requireNonNull(process);  // Throws NPE if null
}

Stack Trace

Caused by: java.lang.NullPointerException
    at java.base/java.util.Objects.requireNonNull(Objects.java:209)
    at org.apache.accumulo.miniclusterImpl.ProcessReference.<init>(ProcessReference.java:30)
    at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
    at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:992)
    at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
    at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
    at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
    at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
    at org.apache.accumulo.miniclusterImpl.MiniAccumuloClusterImpl.references(MiniAccumuloClusterImpl.java:776)
    at org.apache.accumulo.miniclusterImpl.MiniAccumuloClusterImpl.getProcesses(MiniAccumuloClusterImpl.java:782)

Proposed Fix

Add null check for managerProcess consistent with handling of zooKeeperProcess and gcProcess:

public Map<ServerType,Collection<ProcessReference>> getProcesses() {
    Map<ServerType,Collection<ProcessReference>> result = new HashMap<>();
    MiniAccumuloClusterControl control = getClusterControl();
    if (control.managerProcess != null) {  // ADD NULL CHECK
      result.put(ServerType.MANAGER, references(control.managerProcess));
    }
    result.put(ServerType.TABLET_SERVER,
        references(control.tabletServerProcesses.toArray(new Process[0])));
    if (control.zooKeeperProcess != null) {
      result.put(ServerType.ZOOKEEPER, references(control.zooKeeperProcess));
    }
    if (control.gcProcess != null) {
      result.put(ServerType.GARBAGE_COLLECTOR, references(control.gcProcess));
    }
    return result;
}

Additional context
Happy to send a PR for this