diff --git a/.travis.yml b/.travis.yml
index f47ec42..6d4cc50 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,6 +8,8 @@ env:
 
 matrix:
   include:
+    - php: 5.6
+      env: DB=MYSQL RECIPE_VERSION=4.3.x-dev PHPUNIT_TEST=1
     - php: 7.1
       env: DB=MYSQL RECIPE_VERSION=4.3.x-dev PHPCS_TEST=1 PHPUNIT_TEST=1
     - php: 7.1
@@ -17,7 +19,7 @@ matrix:
     - php: 7.2
       env: DB=MYSQL RECIPE_VERSION=4.4.x-dev PHPUNIT_TEST=1
     - php: 7.3
-      env: DB=MYSQL RECIPE_VERSION=4.x-dev
+      env: DB=MYSQL RECIPE_VERSION=4.x-dev PHPUNIT_TEST=1
 
 before_script:
   # Init PHP
diff --git a/src/RestfulServer.php b/src/RestfulServer.php
index 716d5f6..ffccf0f 100644
--- a/src/RestfulServer.php
+++ b/src/RestfulServer.php
@@ -905,11 +905,11 @@ class RestfulServer extends Controller
      * @param HTTPRequest $request
      * @return string
      */
-    protected function resolveClassName(HTTPRequest $request): string
+    protected function resolveClassName(HTTPRequest $request)
     {
         $className = $request->param('ClassName');
         $aliases = self::config()->get('endpoint_aliases');
 
-        return $aliases[$className] ?? $this->unsanitiseClassName($className);
+        return empty($aliases[$className]) ? $this->unsanitiseClassName($className) : $aliases[$className];
     }
 }