(PE-39429) Use correct targets and only run if those targets are non-empty. This fixes errors about run_command needing 3 args when no compilers are present

Author: jhbuchanan45

plans/convert.pp

@@ -305,10 +305,14 @@
     # Restart cluster compiler services that are likely not restarted by our
     # final Puppet run to increase chance everything is functional upon plan
     # completion
-    run_command('systemctl restart pe-puppetserver.service', $legacy_compiler_targets)
+    if $legacy_compiler_targets {
+      run_command('systemctl restart pe-puppetserver.service', $legacy_compiler_targets)
+    }
 
     # PuppetDB is only found on modern compilers, not legacy ones
-    run_command('systemctl restart pe-puppetdb.service pe-puppetserver.service', $compiler_hosts)
+    if $compiler_targets {
+      run_command('systemctl restart pe-puppetserver.service pe-puppetdb.service', $compiler_targets)
+    }
 
     # Run puppet on all targets again to ensure everything is fully up-to-date
     run_task('peadm::puppet_runonce', $all_targets)