FIX #31890 store empty line extrafields (#32152)

* FIX #31890 store empty line extrafields

If a line extrafield had originally some contents, after deleting it and submitting it as empty, the extrafield was not stored but the original contents kept

* corrected whitespace

htdocs/core/class/extrafields.class.php

@@ -11,6 +11,7 @@
  * Copyright (C) 2017       Nicolas ZABOURI         <[email protected]>
  * Copyright (C) 2018-2022  Frédéric France         <[email protected]>
  * Copyright (C) 2022 		Antonin MARCHAL         <[email protected]>
+ * Copyright (C) 2024		Joachim Kueter			<[email protected]>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -2415,10 +2416,13 @@ public function getOptionalsFromPost($extrafieldsobjectkey, $keyprefix = '', $ke
 					}
 					$value_key = dol_htmlcleanlastbr(GETPOST($keysuffix."options_".$key.$keyprefix, 'restricthtml'));
 				} else {
-					if (!GETPOST($keysuffix."options_".$key.$keyprefix)) {
+					if (!GETPOSTISSET($keysuffix."options_".$key.$keyprefix)) {
 						continue; // Value was not provided, we should not set it.
 					}
 					$value_key = GETPOST($keysuffix."options_".$key.$keyprefix);
+					if ($value_key === '') {
+						$value_key = null;
+					}
 				}
 
 				$array_options[$keysuffix."options_".$key] = $value_key; // No keyprefix here. keyprefix is used only for read.