Add union types

Author: nicolas-grekas

Util/IntlTestHelper.php

@@ -30,7 +30,7 @@ class IntlTestHelper
     /**
      * Should be called before tests that work fine with the stub implementation.
      */
-    public static function requireIntl(TestCase $testCase, $minimumIcuVersion = null)
+    public static function requireIntl(TestCase $testCase, string $minimumIcuVersion = null)
     {
         if (null === $minimumIcuVersion) {
             $minimumIcuVersion = Intl::getIcuStubVersion();
@@ -64,7 +64,7 @@ public static function requireIntl(TestCase $testCase, $minimumIcuVersion = null
      * Should be called before tests that require a feature-complete intl
      * implementation.
      */
-    public static function requireFullIntl(TestCase $testCase, $minimumIcuVersion = null)
+    public static function requireFullIntl(TestCase $testCase, string $minimumIcuVersion = null)
     {
         // We only run tests if the intl extension is loaded...
         if (!Intl::isExtensionLoaded()) {