use return value instead of reference parameter

app/code/Magento/Catalog/Ui/Component/Listing/Columns/Price.php

@@ -45,9 +45,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             $store = $this->storeManager->getStore(
@@ -64,5 +64,7 @@ public function prepareDataSource(array & $dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Catalog/Ui/Component/Listing/Columns/ProductActions.php

@@ -42,9 +42,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array &$dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             $storeId = $this->context->getFilterParam('store_id');
@@ -60,5 +60,7 @@ public function prepareDataSource(array &$dataSource)
                 ];
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Catalog/Ui/Component/Listing/Columns/Thumbnail.php

@@ -39,9 +39,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             $fieldName = $this->getData('name');
@@ -58,6 +58,8 @@ public function prepareDataSource(array & $dataSource)
                 $item[$fieldName . '_orig_src'] = $origImageHelper->getUrl();
             }
         }
+
+        return $dataSource;
     }
 
     /**

app/code/Magento/Catalog/Ui/Component/Listing/Columns/Websites.php

@@ -44,7 +44,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         $websiteNames = [];
         foreach ($this->getData('options') as $website) {
@@ -60,6 +60,8 @@ public function prepareDataSource(array & $dataSource)
                 $item[$fieldName] = implode(', ', $websites);
             }
         }
+
+        return $dataSource;
     }
 
     /**

app/code/Magento/Cms/Test/Unit/Ui/Component/Listing/Column/PageActionsTest.php

@@ -81,7 +81,7 @@ public function testPrepareItemsByPageId()
             );
 
         $model->setName($name);
-        $model->prepareDataSource($items);
+        $items = $model->prepareDataSource($items);
         // Run test
         $this->assertEquals($expectedItems, $items['data']['items']);
     }

app/code/Magento/Cms/Ui/Component/Listing/Column/BlockActions.php

@@ -55,9 +55,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -98,5 +98,7 @@ public function prepareDataSource(array & $dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Cms/Ui/Component/Listing/Column/PageActions.php

@@ -59,9 +59,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -92,5 +92,7 @@ public function prepareDataSource(array & $dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Customer/Test/Unit/Ui/Component/Listing/Column/ActionsTest.php

@@ -90,7 +90,7 @@ public function testPrepareDataSource()
             )
             ->willReturn('http://magento.com/customer/index/edit');
 
-        $this->component->prepareDataSource($dataSource);
+        $dataSource = $this->component->prepareDataSource($dataSource);
 
         $this->assertEquals($expectedDataSource, $dataSource);
     }

app/code/Magento/Customer/Test/Unit/Ui/Component/Listing/Column/AttributeColumnTest.php

@@ -62,19 +62,6 @@ public function setup()
         $this->component->setData('name', 'gender');
     }
 
-    public function testPrepareDataSourceWithoutItems()
-    {
-        $dataSource = [
-            'data' => [
-
-            ]
-        ];
-        $this->attributeRepository->expects($this->never())
-            ->method('getMetadataByCode');
-
-        $this->assertNull($this->component->prepareDataSource($dataSource));
-    }
-
     public function testPrepareDataSource()
     {
         $genderOptionId = 1;
@@ -125,7 +112,7 @@ public function testPrepareDataSource()
                 'is_searchable_in_grid' => true,
             ]);
 
-        $this->component->prepareDataSource($dataSource);
+        $dataSource = $this->component->prepareDataSource($dataSource);
 
         $this->assertEquals($expectedSource, $dataSource);
     }

app/code/Magento/Customer/Ui/Component/Listing/Column/Actions.php

@@ -42,9 +42,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array &$dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             $storeId = $this->context->getFilterParam('store_id');
@@ -60,5 +60,7 @@ public function prepareDataSource(array &$dataSource)
                 ];
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Customer/Ui/Component/Listing/Column/AttributeColumn.php

@@ -38,14 +38,10 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array &$dataSource)
+    public function prepareDataSource(array $dataSource)
     {
-        if (!isset($dataSource['data']['items'])) {
-            return null;
-        }
-
         $metaData = $this->attributeRepository->getMetadataByCode($this->getName());
         if ($metaData && count($metaData[AttributeMetadata::OPTIONS])) {
             foreach ($dataSource['data']['items'] as &$item) {
@@ -60,5 +56,7 @@ public function prepareDataSource(array &$dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Customer/Ui/Component/Listing/Column/Online/Type.php

@@ -19,7 +19,7 @@ class Type extends Column
      * @param array $dataSource
      * @return void
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -28,5 +28,7 @@ public function prepareDataSource(array & $dataSource)
                     : __('Customer');
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/AddressTest.php

@@ -39,7 +39,7 @@ public function testPrepareDataSource()
         ];
 
         $this->model->setData('name', $itemName);
-        $this->model->prepareDataSource($dataSource);
+        $dataSource = $this->model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/CustomerGroupTest.php

@@ -57,7 +57,7 @@ public function testPrepareDataSource()
             ->willReturn($group);
 
         $this->model->setData('name', $itemName);
-        $this->model->prepareDataSource($dataSource);
+        $dataSource = $this->model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/OrderActionsTest.php

@@ -63,7 +63,7 @@ public function testPrepareDataSource()
             ->willReturn($url);
 
         $this->model->setData('name', $itemName);
-        $this->model->prepareDataSource($dataSource);
+        $dataSource = $this->model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/PaymentMethodTest.php

@@ -57,7 +57,7 @@ public function testPrepareDataSource()
             ->willReturn($payment);
 
         $this->model->setData('name', $itemName);
-        $this->model->prepareDataSource($dataSource);
+        $dataSource = $this->model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/PriceTest.php

@@ -53,7 +53,7 @@ public function testPrepareDataSource()
             ->willReturn($newItemValue);
 
         $this->model->setData('name', $itemName);
-        $this->model->prepareDataSource($dataSource);
+        $dataSource = $this->model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Test/Unit/Ui/Component/Listing/Column/StatusTest.php

@@ -48,7 +48,7 @@ public function testPrepareDataSource()
             ['collectionFactory' => $collectionFactoryMock]
         );
         $model->setData('name', $itemName);
-        $model->prepareDataSource($dataSource);
+        $dataSource = $model->prepareDataSource($dataSource);
         $this->assertEquals($newItemValue, $dataSource['data']['items'][0][$itemName]);
     }
 }

app/code/Magento/Sales/Ui/Component/Listing/Column/Address.php

@@ -19,14 +19,16 @@ class Address extends Column
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
                 $item[$this->getData('name')] = str_replace("\n", '<br/>', $item[$this->getData('name')]);
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Sales/Ui/Component/Listing/Column/Creditmemo/State.php

@@ -44,9 +44,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -55,5 +55,7 @@ public function prepareDataSource(array & $dataSource)
                     : $item[$this->getData('name')];
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Sales/Ui/Component/Listing/Column/CustomerGroup.php

@@ -46,9 +46,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -62,5 +62,7 @@ public function prepareDataSource(array & $dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Sales/Ui/Component/Listing/Column/Invoice/State.php

@@ -44,9 +44,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -55,5 +55,7 @@ public function prepareDataSource(array & $dataSource)
                     : $item[$this->getData('name')];
             }
         }
+
+        return $dataSource;
     }
 }

app/code/Magento/Sales/Ui/Component/Listing/Column/OrderActions.php

@@ -49,9 +49,9 @@ public function __construct(
      * Prepare Data Source
      *
      * @param array $dataSource
-     * @return void
+     * @return array
      */
-    public function prepareDataSource(array & $dataSource)
+    public function prepareDataSource(array $dataSource)
     {
         if (isset($dataSource['data']['items'])) {
             foreach ($dataSource['data']['items'] as & $item) {
@@ -70,5 +70,7 @@ public function prepareDataSource(array & $dataSource)
                 }
             }
         }
+
+        return $dataSource;
     }
 }