Del: deprecation warnings (#20)

Co-authored-by: Richard Brinkman <[email protected]>

Mail.php

@@ -153,7 +153,7 @@ protected function _sanitizeHeaders(&$headers)
         foreach ($headers as $key => $value) {
             $headers[$key] =
                 preg_replace('=((<CR>|<LF>|0x0A/%0A|0x0D/%0D|\\n|\\r)\S).*=i',
-                             null, $value);
+                             '', $value);
         }
     }
 

Mail/smtp.php

@@ -38,7 +38,7 @@
  *
  * @category    HTTP
  * @package     HTTP_Request
- * @author      Jon Parise <[email protected]> 
+ * @author      Jon Parise <[email protected]>
  * @author      Chuck Hagenbuch <[email protected]>
  * @copyright   2010-2017 Chuck Hagenbuch
  * @license     http://opensource.org/licenses/BSD-3-Clause New BSD License
@@ -299,7 +299,7 @@ protected function send_or_fail($recipients, $headers, $body)
                                     PEAR_MAIL_SMTP_ERROR_FROM);
         }
 
-        $params = null;
+        $params = '';
         if (!empty($this->_extparams)) {
             foreach ($this->_extparams as $key => $val) {
                 $params .= ' ' . $key . (is_null($val) ? '' : '=' . $val);