diff --git a/core/metamodel.class.php b/core/metamodel.class.php
index c70ee91d4..59cfe3f2f 100644
--- a/core/metamodel.class.php
+++ b/core/metamodel.class.php
@@ -7718,15 +7718,15 @@ abstract class MetaModel
 	/**
 	 * @param string $sClass
 	 * @param string $sAttCode
-	 * @param string $sValue
+	 * @param string|null $sValue Code of the state value, can be null if allowed by the attribute definition
 	 *
 	 * @return \ormStyle|null
 	 * @throws \Exception
 	 * @throws \CoreException
 	 */
-	public static function GetEnumStyle(string $sClass, string $sAttCode, string $sValue = ''): ?ormStyle
+	public static function GetEnumStyle(string $sClass, string $sAttCode, ?string $sValue = ''): ?ormStyle
 	{
-		if (empty($sAttCode)) {
+		if (strlen($sAttCode) === 0) {
 			return null;
 		}
 
diff --git a/sources/application/UI/Base/Layout/Object/ObjectDetails.php b/sources/application/UI/Base/Layout/Object/ObjectDetails.php
index 6154ce507..1bf5d336c 100644
--- a/sources/application/UI/Base/Layout/Object/ObjectDetails.php
+++ b/sources/application/UI/Base/Layout/Object/ObjectDetails.php
@@ -59,7 +59,7 @@ class ObjectDetails extends Panel implements iKeyboardShortcut
 	protected $sObjectMode;
 	/** @var string */
 	protected $sIconUrl;
-	/** @var string Code of the current value of the attribute carrying the state for $sClassName */
+	/** @var string|null Code of the current value of the attribute carrying the state for $sClassName */
 	protected $sStatusCode;
 	/** @var string Label of the current value of the attribute carrying the state for $sClassName  */
 	protected $sStatusLabel;
diff --git a/sources/application/UI/Helper/UIHelper.php b/sources/application/UI/Helper/UIHelper.php
index 83ac99f52..ec72ff852 100644
--- a/sources/application/UI/Helper/UIHelper.php
+++ b/sources/application/UI/Helper/UIHelper.php
@@ -19,12 +19,12 @@ namespace Combodo\iTop\Application\UI\Helper;
 class UIHelper
 {
 	/**
-	 * @param string $sStateCode Code of the state value
+	 * @param string|null $sStateCode Code of the state value, can be null if allowed by the attribute definition
 	 * @param bool $bAllowFallbackIfNoMatch If set to true, a fallback semantic color code will be returned in case of no matching mappping. Otherwise it will return null to indicate there was no match.
 	 *
 	 * @return string|null A semantic status color name (eg. success, pending, failure, neutral, ...) depending on the value's code. Usefull to try to find a semantic match when a class has no style defined on its state attribute.
 	 */
-	public static function GetColorNameFromStatusCode(string $sStateCode, bool $bAllowFallbackIfNoMatch = true): ?string
+	public static function GetColorNameFromStatusCode(?string $sStateCode, bool $bAllowFallbackIfNoMatch = true): ?string
 	{
 		$sStatusColor = null;