N°1827 fix freeze on object creation when changing dependant field, if object has hidden TagSet field

application/wizardhelper.class.inc.php

@@ -176,7 +176,15 @@ class WizardHelper
 				}
 				else if ($oAttDef instanceof AttributeTagSet) // AttributeDate is derived from AttributeDateTime
 				{
-					$value = json_decode($value, true);
+					if (is_null($value))
+					{
+						// happens if field is hidden (see N°1827)
+						$value = array();
+					}
+					else
+					{
+						$value = json_decode($value, true);
+					}
 					$oTagSet = new ormTagSet(get_class($oObj), $sAttCode, $oAttDef->GetMaxItems());
 					$oTagSet->SetValues($value['orig_value']);
 					$oTagSet->ApplyDelta($value);

core/ormtagset.class.inc.php

@@ -49,6 +49,10 @@ final class ormTagSet extends ormSet
 	 */
 	public function SetValues($aTagCodes)
 	{
+		if (is_null($aTagCodes))
+		{
+			$aTagCodes = array();
+		}
 		if (!is_array($aTagCodes))
 		{
 			throw new CoreUnexpectedValue("Wrong value {$aTagCodes} for {$this->sClass}:{$this->sAttCode}");