[TASK] Improve PHPDoc of GeneralUtility::_GP

The PHPDoc of GeneralUtility::_GP has been revised.
In detail, the outdated and misleading part about security
has been removed and the return annotation now also
includes NULL as possible return type.

Resolves: #89222
Releases: master, 9.5
Change-Id: Iccfbfc43b15b28c035f5e93805d41e858b816d6a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61743
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>

typo3/sysext/core/Classes/Utility/GeneralUtility.php

@@ -138,12 +138,11 @@ class GeneralUtility
      *
      *************************/
     /**
-     * Returns the 'GLOBAL' value of incoming data from POST or GET, with priority to POST (that is equalent to 'GP' order)
-     * To enhance security in your scripts, please consider using GeneralUtility::_GET or GeneralUtility::_POST if you already
-     * know by which method your data is arriving to the scripts!
+     * Returns the 'GLOBAL' value of incoming data from POST or GET, with priority to POST, which is equalent to 'GP' order
+     * In case you already know by which method your data is arriving consider using GeneralUtility::_GET or GeneralUtility::_POST.
      *
      * @param string $var GET/POST var to return
-     * @return mixed POST var named $var and if not set, the GET var of the same name.
+     * @return mixed POST var named $var, if not set, the GET var of the same name and if also not set, NULL.
      */
     public static function _GP($var)
     {