Populate link fields only with URI if value is a string

src/Drupal/Driver/Fields/Drupal8/LinkHandler.php

@@ -16,14 +16,18 @@ public function expand($values) {
       // 'options' is required to be an array, otherwise the utility class
       // Drupal\Core\Utility\UnroutedUrlAssembler::assemble() will complain.
       $options = [];
+      // Instantiate the value as URI-only if $value is a string.
+      if (is_string($value)) {
+        $value = [NULL, $value];
+      }
       if (!empty($value[2])) {
         parse_str($value[2], $options);
       }
-      $return[] = [
+      $return[] = array_filter([
         'options' => $options,
         'title' => $value[0],
         'uri' => $value[1],
-      ];
+      ], fn ($value) => !is_null($value));
     }
     return $return;
   }

tests/Drupal/Tests/Driver/Field/LinkHandlerTest.php

@@ -0,0 +1,136 @@
+<?php
+
+namespace Drupal\Tests\Driver\Field;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Entity\EntityFieldManagerInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Driver\Fields\Drupal8\LinkHandler;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests LinkHandler.
+ *
+ * @coversDefaultClass \Drupal\Driver\Fields\Drupal8\LinkHandler
+ */
+class LinkHandlerTest extends TestCase {
+
+  const TEST_ENTITY_TYPE_ID = 'test_entity';
+  const TEST_FIELD_ID = 'test_field';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $entityType = $this->getMockBuilder(EntityTypeInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entityType->method('getKey')
+      ->with('bundle')
+      ->willReturn('bundle');
+
+    $entityTypeManager = $this->getMockBuilder(EntityTypeManagerInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entityTypeManager->method('getDefinition')
+      ->with(self::TEST_ENTITY_TYPE_ID)
+      ->willReturn($entityType);
+
+    $fieldDefinition = $this->getMockBuilder(FieldDefinitionInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entityFieldManager = $this->getMockBuilder(EntityFieldManagerInterface::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $entityFieldManager->method('getFieldStorageDefinitions')
+      ->with(self::TEST_ENTITY_TYPE_ID)
+      ->willReturn([
+        self::TEST_FIELD_ID => [],
+      ]);
+    $entityFieldManager->method('getFieldDefinitions')
+      ->with(self::TEST_ENTITY_TYPE_ID, self::TEST_ENTITY_TYPE_ID)
+      ->willReturn([
+        self::TEST_FIELD_ID => $fieldDefinition,
+      ]);
+
+    $container = new ContainerBuilder();
+    $container->set('entity_type.manager', $entityTypeManager);
+    $container->set('entity_field.manager', $entityFieldManager);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * @covers ::expand
+   *
+   * @dataProvider providerTestLinkHandler
+   */
+  public function testLinkHandler(array $values, array $expected): void {
+    $entityObject = [
+      'bundle' => self::TEST_ENTITY_TYPE_ID,
+      self::TEST_FIELD_ID => $values,
+    ];
+    $linkHandler = new LinkHandler(
+      (object) $entityObject,
+      self::TEST_ENTITY_TYPE_ID,
+      self::TEST_FIELD_ID,
+    );
+
+    $this->assertSame($expected, $linkHandler->expand($entityObject[self::TEST_FIELD_ID]));
+  }
+
+  /**
+   * Data provider for ::testLinkHandler.
+   *
+   * @return array[][]
+   *   The test cases.
+   */
+  public function providerTestLinkHandler(): array {
+    return [
+      'Link with only URI' => [
+        'values' => [
+          'https://example.com',
+        ],
+        'expected' => [
+          [
+            'options' => [],
+            'uri' => 'https://example.com',
+          ],
+        ],
+      ],
+      'Link with title and URI' => [
+        'values' => [
+          ['Link title', 'https://example.com'],
+        ],
+        'expected' => [
+          [
+            'options' => [],
+            'title' => 'Link title',
+            'uri' => 'https://example.com',
+          ],
+        ],
+      ],
+      'A link with title and another with only URI' => [
+        'values' => [
+          'https://example.com/first',
+          ['Second link', 'https://example.com/second'],
+        ],
+        'expected' => [
+          [
+            'options' => [],
+            'uri' => 'https://example.com/first',
+          ],
+          [
+            'options' => [],
+            'title' => 'Second link',
+            'uri' => 'https://example.com/second',
+          ],
+        ],
+      ],
+    ];
+  }
+
+}