diff -u b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeFieldItemList.php b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeFieldItemList.php
--- b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeFieldItemList.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeFieldItemList.php
@@ -61,9 +61,9 @@
           '#states' => array(
             'visible' => array(
               ':input[id="edit-default-value-input-default-date-type"]' => array('value' => static::DEFAULT_VALUE_CUSTOM),
-            ),
-          ),
-        ),
+            )
+          )
+        )
       );
 
       if ($this->getFieldDefinition()->getSetting('enddate_get')) {
@@ -149,27 +149,28 @@
    */
   public static function processDefaultValue($default_value, FieldableEntityInterface $entity, FieldDefinitionInterface $definition) {
     $default_value = parent::processDefaultValue($default_value, $entity, $definition);
-    $default_date_type2 = $default_value[0]['default_date_type2'];
+
+    $return = array();
 
     if (isset($default_value[0]['default_date_type'])) {
       // A default value should be in the format and timezone used for date
       // storage.
       $date = new DrupalDateTime($default_value[0]['default_date'], DATETIME_STORAGE_TIMEZONE);
-      $storage_format = $definition->getSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE ? DATETIME_DATE_STORAGE_FORMAT : DATETIME_DATETIME_STORAGE_FORMAT;
+      $storage_format = $definition->getSetting('datetime_type') == DateTimeItem::DATETIME_TYPE_DATE ? DATETIME_DATE_STORAGE_FORMAT: DATETIME_DATETIME_STORAGE_FORMAT;
       $value = $date->format($storage_format);
       // We only provide a default value for the first item, as do all fields.
       // Otherwise, there is no way to clear out unwanted values on multiple value
       // fields.
-      $default_value =  array(
+      $return = array(
         array(
           'value' => $value,
           'date' => $date,
-        ),
+        )
       );
-      }
+    }
 
     // Repeat for end date.
-    if ($definition->getSetting('enddate_get') && !empty($default_date_type2)) {
+    if ($definition->getSetting('enddate_get') && !empty($default_value[0]['default_date_type2'])) {
       // A default value should be in the format and timezone used for date
       // storage.
       $date = new DrupalDateTime($default_value[0]['default_date2'], DATETIME_STORAGE_TIMEZONE);
@@ -178,12 +179,12 @@
       // We only provide a default value for the first item, as do all fields.
       // Otherwise, there is no way to clear out unwanted values on multiple value
       // fields.
-      $default_value[0] += array(
+      $return[0] += array(
         'value2' => $value,
         'date2' => $date,
       );
     }
-    return $default_value;
+    return empty($return) ? $default_value : $return;
   }
 
 }