diff --git a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
index 8a0cfd3752..2aa402ffa0 100644
--- a/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
+++ b/core/lib/Drupal/Core/Field/BaseFieldDefinition.php
@@ -576,11 +576,11 @@ public function setInitialValue($value) {
   /**
    * Returns the name of the field that will be used for getting initial values.
    *
-   * @return array
-   *   An array containing the name of the field and a default value.
+   * @return string|null
+   *   The field name.
    */
   public function getInitialValueFromField() {
-    return isset($this->definition['initial_value_from_field']) ? $this->definition['initial_value_from_field'] : [];
+    return isset($this->definition['initial_value_from_field']) ? $this->definition['initial_value_from_field'] : NULL;
   }
 
   /**