Giving the possibility to have a config dependency based on empty field value

Author: eduard13

app/code/Magento/Config/Model/Config/Structure/Element/Dependency/Field.php

@@ -41,7 +41,7 @@ public function __construct(array $fieldData = [], $fieldPrefix = "")
         if (isset($fieldData['separator'])) {
             $this->_values = explode($fieldData['separator'], $fieldData['value']);
         } else {
-            $this->_values = [$fieldData['value']];
+            $this->_values = [isset($fieldData['value']) ? $fieldData['value'] : ''];
         }
         $fieldId = $fieldPrefix . (isset(
             $fieldData['dependPath']

app/code/Magento/Config/Test/Unit/Model/Config/Structure/Element/Dependency/FieldTest.php

@@ -12,6 +12,8 @@ class FieldTest extends \PHPUnit\Framework\TestCase
      */
     const SIMPLE_VALUE = 'someValue';
 
+    const EMPTY_VALUE = '';
+
     const COMPLEX_VALUE1 = 'value_1';
 
     const COMPLEX_VALUE2 = 'value_2';
@@ -150,8 +152,19 @@ public function getValuesDataProvider()
         return [
             [$this->_getSimpleData(), true, [self::SIMPLE_VALUE]],
             [$this->_getSimpleData(), false, [self::SIMPLE_VALUE]],
+            [$this->_getSimpleEmptyData(), false, [static::EMPTY_VALUE]],
             [$this->_getComplexData(), true, $complexDataValues],
             [$this->_getComplexData(), false, $complexDataValues]
         ];
     }
+
+    /**
+     * Providing a field data with no field value
+     *
+     * @return array
+     */
+    protected function _getSimpleEmptyData(): array
+    {
+        return ['dependPath' => ['section_2', 'group_3', 'field_4']];
+    }
 }