diff --git a/framework/base/Model.php b/framework/base/Model.php
index 085ec1a..bbbb0d2 100644
--- a/framework/base/Model.php
+++ b/framework/base/Model.php
@@ -617,7 +617,7 @@ class Model extends Component implements StaticInstanceInterface, IteratorAggreg
     /**
      * Returns the first error of the specified attribute.
      * @param string $attribute attribute name.
-     * @return string the error message. Null is returned if no error.
+     * @return string|null the error message. Null is returned if no error.
      * @see getErrors()
      * @see getFirstErrors()
      */
diff --git a/framework/data/Pagination.php b/framework/data/Pagination.php
index f593d9a..247d907 100644
--- a/framework/data/Pagination.php
+++ b/framework/data/Pagination.php
@@ -340,7 +340,7 @@ class Pagination extends BaseObject implements Linkable
      * This method returns the named parameter value from [[params]]. Null is returned if the value does not exist.
      * @param string $name the parameter name
      * @param string $defaultValue the value to be returned when the specified parameter does not exist in [[params]].
-     * @return string the parameter value
+     * @return string|null the parameter value
      */
     protected function getQueryParam($name, $defaultValue = null)
     {
diff --git a/framework/db/Connection.php b/framework/db/Connection.php
index 25ad2ec..2ea8224 100644
--- a/framework/db/Connection.php
+++ b/framework/db/Connection.php
@@ -881,7 +881,7 @@ class Connection extends Component
      * Obtains the schema information for the named table.
      * @param string $name table name.
      * @param bool $refresh whether to reload the table schema even if it is found in the cache.
-     * @return TableSchema table schema information. Null if the named table does not exist.
+     * @return TableSchema|null table schema information. Null if the named table does not exist.
      */
     public function getTableSchema($name, $refresh = false)
     {
diff --git a/framework/db/TableSchema.php b/framework/db/TableSchema.php
index 899ddb8..71a2350 100644
--- a/framework/db/TableSchema.php
+++ b/framework/db/TableSchema.php
@@ -64,7 +64,7 @@ class TableSchema extends BaseObject
      * Gets the named column metadata.
      * This is a convenient method for retrieving a named column even if it does not exist.
      * @param string $name column name
-     * @return ColumnSchema metadata of the named column. Null if the named column does not exist.
+     * @return ColumnSchema|null metadata of the named column. Null if the named column does not exist.
      */
     public function getColumn($name)
     {
diff --git a/framework/helpers/BaseFileHelper.php b/framework/helpers/BaseFileHelper.php
index 71bfe8f..4fa96cf 100644
--- a/framework/helpers/BaseFileHelper.php
+++ b/framework/helpers/BaseFileHelper.php
@@ -146,7 +146,7 @@ class BaseFileHelper
      * and this is null, it will use the file specified by [[mimeMagicFile]].
      * @param bool $checkExtension whether to use the file extension to determine the MIME type in case
      * `finfo_open()` cannot determine it.
-     * @return string the MIME type (e.g. `text/plain`). Null is returned if the MIME type cannot be determined.
+     * @return string|null the MIME type (e.g. `text/plain`). Null is returned if the MIME type cannot be determined.
      * @throws InvalidConfigException when the `fileinfo` PHP extension is not installed and `$checkExtension` is `false`.
      */
     public static function getMimeType($file, $magicFile = null, $checkExtension = true)
diff --git a/framework/rbac/BaseManager.php b/framework/rbac/BaseManager.php
index 60cbc01..48d7b3f 100644
--- a/framework/rbac/BaseManager.php
+++ b/framework/rbac/BaseManager.php
@@ -37,7 +37,7 @@ abstract class BaseManager extends Component implements ManagerInterface
     /**
      * Returns the named auth item.
      * @param string $name the auth item name.
-     * @return Item the auth item corresponding to the specified name. Null is returned if no such item.
+     * @return Item|null the auth item corresponding to the specified name. Null is returned if no such item.
      */
     abstract protected function getItem($name);
 
diff --git a/framework/web/CookieCollection.php b/framework/web/CookieCollection.php
index c26cfd3..aaedd9b 100644
--- a/framework/web/CookieCollection.php
+++ b/framework/web/CookieCollection.php
@@ -83,7 +83,7 @@ class CookieCollection extends BaseObject implements \IteratorAggregate, \ArrayA
     /**
      * Returns the cookie with the specified name.
      * @param string $name the cookie name
-     * @return Cookie the cookie with the specified name. Null if the named cookie does not exist.
+     * @return Cookie|null the cookie with the specified name. Null if the named cookie does not exist.
      * @see getValue()
      */
     public function get($name)
diff --git a/framework/web/HeaderCollection.php b/framework/web/HeaderCollection.php
index 1fa6021..ee33a27 100644
--- a/framework/web/HeaderCollection.php
+++ b/framework/web/HeaderCollection.php
@@ -141,7 +141,7 @@ class HeaderCollection extends BaseObject implements \IteratorAggregate, \ArrayA
     /**
      * Removes a header.
      * @param string $name the name of the header to be removed.
-     * @return array the value of the removed header. Null is returned if the header does not exist.
+     * @return array|null the value of the removed header. Null is returned if the header does not exist.
      */
     public function remove($name)
     {