Issue #3172166 by Pooja Ganjage, ekes, Megha_kundar, xjm, alexpott,...

Issue #3172166 by Pooja Ganjage, ekes, Megha_kundar, xjm, alexpott, tstoeckler, mbovan, Spokje: Element::properties() produces notices if given an array with integer keys

core/lib/Drupal/Core/Render/Element.php

@@ -24,7 +24,7 @@ class Element {
    *   TRUE of the key is a property, FALSE otherwise.
    */
   public static function property($key) {
-    return $key[0] == '#';
+    return is_string($key) && $key[0] == '#';
   }
 
   /**

core/tests/Drupal/Tests/Core/Render/ElementTest.php

@@ -19,6 +19,7 @@ public function testProperty() {
     $this->assertTrue(Element::property('#property'));
     $this->assertFalse(Element::property('property'));
     $this->assertFalse(Element::property('property#'));
+    $this->assertFalse(Element::property(0));
   }
 
   /**
@@ -29,13 +30,12 @@ public function testProperties() {
       '#property1' => 'property1',
       '#property2' => 'property2',
       'property3' => 'property3',
+      0 => [],
     ];
 
     $properties = Element::properties($element);
 
-    $this->assertContains('#property1', $properties);
-    $this->assertContains('#property2', $properties);
-    $this->assertNotContains('property3', $properties);
+    $this->assertSame(['#property1', '#property2'], $properties);
   }
 
   /**