diff --git a/core/tests/Drupal/KernelTests/AssertLegacyTrait.php b/core/tests/Drupal/KernelTests/AssertLegacyTrait.php
index 17a2ea4133..1360798e46 100644
--- a/core/tests/Drupal/KernelTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/KernelTests/AssertLegacyTrait.php
@@ -34,7 +34,7 @@ protected function assert($actual, $message = '') {
    *   instead.
    */
   protected function assertEqual($actual, $expected, $message = '') {
-    $this->assertEquals($expected, $actual, !empty($message) ? $message : '');
+    $this->assertEquals($expected, $actual, (string) $message);
   }
 
   /**
@@ -44,7 +44,7 @@ protected function assertEqual($actual, $expected, $message = '') {
    *   self::assertNotEquals() instead.
    */
   protected function assertNotEqual($actual, $expected, $message = '') {
-    $this->assertNotEquals($expected, $actual, !empty($message) ? $message : '');
+    $this->assertNotEquals($expected, $actual, (string) $message);
   }
 
   /**
@@ -54,7 +54,7 @@ protected function assertNotEqual($actual, $expected, $message = '') {
    *   instead.
    */
   protected function assertIdentical($actual, $expected, $message = '') {
-    $this->assertSame($expected, $actual, !empty($message) ? $message : '');
+    $this->assertSame($expected, $actual, (string) $message);
   }
 
   /**
@@ -64,7 +64,7 @@ protected function assertIdentical($actual, $expected, $message = '') {
    *   self::assertNotSame() instead.
    */
   protected function assertNotIdentical($actual, $expected, $message = '') {
-    $this->assertNotSame($expected, $actual, !empty($message) ? $message : '');
+    $this->assertNotSame($expected, $actual, (string) $message);
   }
 
   /**
@@ -77,7 +77,7 @@ protected function assertIdenticalObject($actual, $expected, $message = '') {
     // Note: ::assertSame checks whether its the same object. ::assertEquals
     // though compares
 
-    $this->assertEquals($expected, $actual, !empty($message) ? $message : '');
+    $this->assertEquals($expected, $actual, (string) $message);
   }
 
   /**