diff --git a/modules/block/block.api.php b/modules/block/block.api.php
index 312eb11..eff6c18 100644
--- a/modules/block/block.api.php
+++ b/modules/block/block.api.php
@@ -200,7 +200,8 @@ function hook_block_save($delta = '', $edit = array()) {
  *   within the module, defined in hook_block_info().
  *
  * @return
- *   An array containing the following elements:
+ *   If the block should not be shown, no return value or an array containing
+ *   the following elements:
  *   - subject: The default localized title of the block. If the block does not
  *     have a default title, this should be set to NULL.
  *   - content: The content of the block's body. This may be a renderable array
@@ -253,12 +254,15 @@ function hook_block_view($delta = '') {
  * specific block.
  *
  * @param $data
- *   An array of data, as returned from the hook_block_view() implementation of
+ *   An array of data or NULL, as returned from the hook_block_view()
+ *   implementation of
  *   the module that defined the block:
  *   - subject: The default localized title of the block.
  *   - content: Either a string or a renderable array representing the content
  *     of the block. You should check that the content is an array before trying
  *     to modify parts of the renderable structure.
+ *   If the block should not be shown, $data may be NULL. Any module
+ *   implementing this hook should check if $data is NULL, before acting on it.
  * @param $block
  *   The block object, as loaded from the database, having the main properties:
  *   - module: The name of the module that defined the block.
@@ -287,12 +291,14 @@ function hook_block_view_alter(&$data, $block) {
  * specific block, rather than implementing hook_block_view_alter().
  *
  * @param $data
- *   An array of data, as returned from the hook_block_view() implementation of
- *   the module that defined the block:
+ *   An array of data or NULL, as returned from the hook_block_view()
+ *   implementation of the module that defined the block:
  *   - subject: The localized title of the block.
  *   - content: Either a string or a renderable array representing the content
  *     of the block. You should check that the content is an array before trying
  *     to modify parts of the renderable structure.
+ *   If the block should not be shown, $data may be NULL. Any module
+ *   implementing this hook should check if $data is NULL, before acting on it.
  * @param $block
  *   The block object, as loaded from the database, having the main properties:
  *   - module: The name of the module that defined the block.