diff --git a/src/unit/engine/ArcanistUnitTestEngine.php b/src/unit/engine/ArcanistUnitTestEngine.php
index ad66bb90..e105f216 100644
--- a/src/unit/engine/ArcanistUnitTestEngine.php
+++ b/src/unit/engine/ArcanistUnitTestEngine.php
@@ -1,118 +1,118 @@
 <?php
 
 /**
  * Manages unit test execution.
  */
 abstract class ArcanistUnitTestEngine extends Phobject {
 
   private $workingCopy;
-  private $paths;
+  private $paths = array();
   private $arguments = array();
   private $enableAsyncTests;
   private $enableCoverage;
   private $runAllTests;
   private $configurationManager;
   protected $renderer;
 
   final public function __construct() {}
 
   public function getEngineConfigurationName() {
     return null;
   }
 
   final public function setRunAllTests($run_all_tests) {
     if (!$this->supportsRunAllTests() && $run_all_tests) {
       throw new Exception(
         pht(
           "Engine '%s' does not support %s.",
           get_class($this),
           '--everything'));
     }
 
     $this->runAllTests = $run_all_tests;
     return $this;
   }
 
   final public function getRunAllTests() {
     return $this->runAllTests;
   }
 
   protected function supportsRunAllTests() {
     return false;
   }
 
   final public function setConfigurationManager(
     ArcanistConfigurationManager $configuration_manager) {
     $this->configurationManager = $configuration_manager;
     return $this;
   }
 
   final public function getConfigurationManager() {
     return $this->configurationManager;
   }
 
   final public function setWorkingCopy(
     ArcanistWorkingCopyIdentity $working_copy) {
 
     $this->workingCopy = $working_copy;
     return $this;
   }
 
   final public function getWorkingCopy() {
     return $this->workingCopy;
   }
 
   final public function setPaths(array $paths) {
     $this->paths = $paths;
     return $this;
   }
 
   final public function getPaths() {
     return $this->paths;
   }
 
   final public function setArguments(array $arguments) {
     $this->arguments = $arguments;
     return $this;
   }
 
   final public function getArgument($key, $default = null) {
     return idx($this->arguments, $key, $default);
   }
 
   final public function setEnableAsyncTests($enable_async_tests) {
     $this->enableAsyncTests = $enable_async_tests;
     return $this;
   }
 
   final public function getEnableAsyncTests() {
     return $this->enableAsyncTests;
   }
 
   final public function setEnableCoverage($enable_coverage) {
     $this->enableCoverage = $enable_coverage;
     return $this;
   }
 
   final public function getEnableCoverage() {
     return $this->enableCoverage;
   }
 
   final public function setRenderer(ArcanistUnitRenderer $renderer) {
     $this->renderer = $renderer;
     return $this;
   }
 
   abstract public function run();
 
   /**
    * Modify the return value of this function in the child class, if you do
    * not need to echo the test results after all the tests have been run. This
    * is the case for example when the child class prints the tests results
    * while the tests are running.
    */
   public function shouldEchoTestResults() {
     return true;
   }
 
 }