diff --git a/htdocs/core/modules/product/mod_codeproduct_elephant.php b/htdocs/core/modules/product/mod_codeproduct_elephant.php
index 644808826d5..397312fbb5f 100644
--- a/htdocs/core/modules/product/mod_codeproduct_elephant.php
+++ b/htdocs/core/modules/product/mod_codeproduct_elephant.php
@@ -118,12 +118,12 @@ class mod_codeproduct_elephant extends ModeleProductCode
 	/**
 	 * Return an example of result returned by getNextValue
 	 *
-	 * @param	Translate	$langs		Object langs
-	 * @param	Product		$objproduct		Object product
-	 * @param	int			$type		Type of third party (1:customer, 2:supplier, -1:autodetect)
-	 * @return	string					Return string example
+	 * @param	Translate		$langs		Object langs
+	 * @param	Product|string	$objproduct	Object product
+	 * @param	int				$type		Type of third party (1:customer, 2:supplier, -1:autodetect)
+	 * @return	string						Return string example
 	 */
-	public function getExample($langs, $objproduct = null, $type = -1)
+	public function getExample($langs, $objproduct = '', $type = -1)
 	{
 		$exampleproduct = $exampleservice = '';
 
diff --git a/htdocs/core/modules/product/mod_codeproduct_leopard.php b/htdocs/core/modules/product/mod_codeproduct_leopard.php
index 990d55b691e..d8ae7f91676 100644
--- a/htdocs/core/modules/product/mod_codeproduct_leopard.php
+++ b/htdocs/core/modules/product/mod_codeproduct_leopard.php
@@ -85,11 +85,11 @@ class mod_codeproduct_leopard extends ModeleProductCode
 	/**
 	 * Return an example of result returned by getNextValue
 	 *
-	 * @param	?Product		$objproduct		Object product
-	 * @param	int			$type		Type of third party (1:customer, 2:supplier, -1:autodetect)
-	 * @return	string					Return next value
+	 * @param	Product|string	$objproduct	Object product
+	 * @param	int				$type		Type of third party (1:customer, 2:supplier, -1:autodetect)
+	 * @return	string						Return next value
 	 */
-	public function getNextValue($objproduct = null, $type = -1)
+	public function getNextValue($objproduct = '', $type = -1)
 	{
 		return '';
 	}
diff --git a/htdocs/core/modules/product/modules_product.class.php b/htdocs/core/modules/product/modules_product.class.php
index 6d9e87bf023..cfe79891429 100644
--- a/htdocs/core/modules/product/modules_product.class.php
+++ b/htdocs/core/modules/product/modules_product.class.php
@@ -64,11 +64,11 @@ abstract class ModeleProductCode extends CommonNumRefGenerator
 	/**
 	 *  Return next value available
 	 *
-	 *	@param	?Product		$objproduct		Object product
-	 *	@param	int			$type		Type
-	 *  @return string      			Value
+	 *	@param	Product|string	$objproduct	Object product
+	 *	@param	int				$type		Type
+	 *  @return string      				Value
 	 */
-	public function getNextValue($objproduct = null, $type = -1)
+	public function getNextValue($objproduct = '', $type = -1)
 	{
 		global $langs;
 		return $langs->trans("Function_getNextValue_InModuleNotWorking");