Merge remote-tracking branch 'origin/MAGETWO-50767' into BUGS

Author: Sergey Semenov

app/code/Magento/Theme/Model/Design/Backend/Theme.php

@@ -87,7 +87,7 @@ protected function invalidateCache($forceInvalidate = false)
      */
     public function getValue()
     {
-        return $this->getData('value') != '' ? $this->getData('value') : null;
+        return $this->getData('value') !== null ? $this->getData('value') : '';
     }
 
     /**

app/code/Magento/Theme/Test/Unit/Model/Design/Backend/ThemeTest.php

@@ -111,6 +111,26 @@ public function testAfterSave($callNumber, $oldValue)
         $this->assertInstanceOf(get_class($this->model), $this->model->afterSave());
     }
 
+    /**
+     * @param string|null $value
+     * @param string $expectedResult
+     * @return void
+     * @dataProvider getValueDataProvider
+     */
+    public function testGetValue($value, $expectedResult)
+    {
+        $this->model->setValue($value);
+        $this->assertEquals($expectedResult, $this->model->getValue());
+    }
+
+    public function getValueDataProvider()
+    {
+        return [
+            [null, ''],
+            ['value', 'value']
+        ];
+    }
+
     public function afterSaveDataProvider()
     {
         return [