[JENKINS-51955] - Prevent NPE in SlaveComputer#setChannel(Channel,OutputStream...

[JENKINS-51955] - Prevent NPE in SlaveComputer#setChannel(Channel,OutputStream launchLog,Channel.Listener,) when null launchLog is passed from API

core/src/main/java/hudson/slaves/SlaveComputer.java

@@ -578,14 +578,18 @@ public class SlaveComputer extends Computer {
 
     /**
      * Sets up the connection through an existing channel.
-     * @param channel the channel to use; <strong>warning:</strong> callers are expected to have called {@link ChannelConfigurator} already
+     * @param channel the channel to use; <strong>warning:</strong> callers are expected to have called {@link ChannelConfigurator} already.
+     * @param launchLog Launch log. If not {@code null}, will receive launch log messages
+     * @param listener Channel event listener to be attached (if not {@code null})
      * @since 1.444
      */
-    public void setChannel(Channel channel, OutputStream launchLog, Channel.Listener listener) throws IOException, InterruptedException {
+    public void setChannel(@Nonnull Channel channel,
+                           @CheckForNull OutputStream launchLog,
+                           @CheckForNull Channel.Listener listener) throws IOException, InterruptedException {
         if(this.channel!=null)
             throw new IllegalStateException("Already connected");
 
-        final TaskListener taskListener = new StreamTaskListener(launchLog);
+        final TaskListener taskListener = launchLog != null ? new StreamTaskListener(launchLog) : TaskListener.NULL;
         PrintStream log = taskListener.getLogger();
 
         channel.setProperty(SlaveComputer.class, this);