diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index a4f73cd6cf2..db05b86c442 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -2721,7 +2721,7 @@ function dol_bc($var, $moreclass = '')
  *      @return string						Formatted string
  *      @see dol_print_address()
  */
-function dol_format_address($object, $withcountry = 0, $sep = "\n", $outputlangs = '', $mode = 0, $extralangcode = '')
+function dol_format_address($object, $withcountry = 0, $sep = "\n", $outputlangs = null, $mode = 0, $extralangcode = '')
 {
 	global $conf, $langs, $hookmanager;
 
@@ -2843,7 +2843,7 @@ function dol_strftime($fmt, $ts = false, $is_gmt = false)
  *
  *  @see        dol_mktime(), dol_stringtotime(), dol_getdate(), selectDate()
  */
-function dol_print_date($time, $format = '', $tzoutput = 'auto', $outputlangs = '', $encodetooutput = false)
+function dol_print_date($time, $format = '', $tzoutput = 'auto', $outputlangs = null, $encodetooutput = false)
 {
 	global $conf, $langs;
 
@@ -8983,7 +8983,7 @@ function complete_substitutions_array(&$substitutionarray, $outputlangs, $object
  *    @param	Translate	$outputlangs   Output language
  *    @return	void
  */
-function print_date_range($date_start, $date_end, $format = '', $outputlangs = '')
+function print_date_range($date_start, $date_end, $format = '', $outputlangs = null)
 {
 	print get_date_range($date_start, $date_end, $format, $outputlangs);
 }
@@ -8998,7 +8998,7 @@ function print_date_range($date_start, $date_end, $format = '', $outputlangs = '
  *    @param	integer		$withparenthesis	1=Add parenthesis, 0=no parenthesis
  *    @return	string							String
  */
-function get_date_range($date_start, $date_end, $format = '', $outputlangs = '', $withparenthesis = 1)
+function get_date_range($date_start, $date_end, $format = '', $outputlangs = null, $withparenthesis = 1)
 {
 	global $langs;