MAGETWO-72624: [2.3] - [Magento Cloud] Unable to clear multiselct in attribute editor.

Author: zakdma

lib/internal/Magento/Framework/Data/Form/Element/Multiselect.php

@@ -61,6 +61,10 @@ public function getElementHtml()
                 <input type="hidden" id="' . $this->getHtmlId() . '_hidden" name="' . parent::getName() . '" value="" />
                 ';
         }
+        if (!empty($this->_data['disabled'])) {
+            $html .= '<input type="hidden" name="' . parent::getName() . '_disabled" value="" />';
+        }
+
         $html .= '<select id="' . $this->getHtmlId() . '" name="' . $this->getName() . '" ' . $this->serialize(
             $this->getHtmlAttributes()
         ) . $this->_getUiId() . ' multiple="multiple">' . "\n";

lib/internal/Magento/Framework/Data/Test/Unit/Form/Element/MultiselectTest.php

@@ -20,9 +20,10 @@ protected function setUp()
     }
 
     /**
-     * Verify that hidden input is present in multiselect
+     * Verify that hidden input is present in multiselect.
      *
      * @covers \Magento\Framework\Data\Form\Element\Multiselect::getElementHtml
+     * @return void
      */
     public function testHiddenFieldPresentInMultiSelect()
     {
@@ -39,7 +40,38 @@ public function testHiddenFieldPresentInMultiSelect()
     }
 
     /**
-     * Verify that js element is added
+     * Verify that hidden input is present in multiselect and it allow indicate is multiselect is disabled.
+     *
+     * @return void
+     */
+    public function testHiddenDisabledFieldPresentInMultiSelect()
+    {
+        $fieldName = 'fieldName';
+        $this->_model->setDisabled(true);
+        $this->_model->setName($fieldName);
+        $elementHtml = $this->_model->getElementHtml();
+        $this->assertContains('<input type="hidden" name="' . $fieldName . '_disabled"', $elementHtml);
+    }
+
+    /**
+     * Verify that hidden input doesn't present in multiselect and it allow indicate is multiselect is disabled.
+     *
+     * @covers \Magento\Framework\Data\Form\Element\Multiselect::getElementHtml
+     * @return void
+     */
+    public function testHiddenDisabledFieldNotPresentInMultiSelect()
+    {
+        $fieldName = 'fieldName';
+        $this->_model->setDisabled(false);
+        $this->_model->setName($fieldName);
+        $elementHtml = $this->_model->getElementHtml();
+        $this->assertNotContains('<input type="hidden" name="' . $fieldName . '_disabled"', $elementHtml);
+    }
+
+    /**
+     * Verify that js element is added.
+     *
+     * @return void
      */
     public function testGetAfterElementJs()
     {