diff --git a/core/asynctask.class.inc.php b/core/asynctask.class.inc.php
index 538ca1f85..4476388f2 100644
--- a/core/asynctask.class.inc.php
+++ b/core/asynctask.class.inc.php
@@ -85,7 +85,7 @@ abstract class AsyncTask extends DBObject
 		// The value is set from null to planned in the setup program
 		MetaModel::Init_AddAttribute(new AttributeEnum("status", array("allowed_values"=>new ValueSetEnum('planned,running,idle,error'), "sql"=>"status", "default_value"=>"planned", "is_null_allowed"=>true, "depends_on"=>array())));
 
-		MetaModel::Init_AddAttribute(new AttributeDateTime("created", array("allowed_values"=>null, "sql"=>"created", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeDateTime("created", array("allowed_values"=>null, "sql"=>"created", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeDateTime("started", array("allowed_values"=>null, "sql"=>"started", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeDateTime("planned", array("allowed_values"=>null, "sql"=>"planned", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeExternalKey("event_id", array("targetclass"=>"Event", "jointype"=> "", "allowed_values"=>null, "sql"=>"event_id", "is_null_allowed"=>true, "on_target_delete"=>DEL_SILENT, "depends_on"=>array())));
diff --git a/core/attributedef.class.inc.php b/core/attributedef.class.inc.php
index dd546d735..d1f9d96cb 100644
--- a/core/attributedef.class.inc.php
+++ b/core/attributedef.class.inc.php
@@ -2510,16 +2510,18 @@ class AttributeDateTime extends AttributeDBField
 		return $iUnixSeconds;
 	}
 
+	// This has been done at the time when itop was using TIMESTAMP columns,
+	// now that iTop is using DATETIME columns, it seems possible to have IsNullAllowed returning false... later when this is needed
+	public function IsNullAllowed() {return true;}
 	public function GetDefaultValue()
 	{
 		$default = parent::GetDefaultValue();
 
-		if (!empty($default))
+		if (!parent::IsNullAllowed())
 		{
-			$iDate = strtotime($default);
-			if ($iDate !== false)
+			if (empty($default))
 			{
-				$default = date($this->GetDateFormat(), $iDate);
+				$default = date($this->GetDateFormat());
 			}
 		}
 
diff --git a/core/cmdbchange.class.inc.php b/core/cmdbchange.class.inc.php
index eec405792..7304db99c 100644
--- a/core/cmdbchange.class.inc.php
+++ b/core/cmdbchange.class.inc.php
@@ -50,7 +50,7 @@ class CMDBChange extends DBObject
 		);
 		MetaModel::Init_Params($aParams);
 		//MetaModel::Init_InheritAttributes();
-		MetaModel::Init_AddAttribute(new AttributeDateTime("date", array("allowed_values"=>null, "sql"=>"date", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeDateTime("date", array("allowed_values"=>null, "sql"=>"date", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("userinfo", array("allowed_values"=>null, "sql"=>"userinfo", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeEnum("origin", array("allowed_values"=>new ValueSetEnum('interactive,csv-interactive,csv-import.php,webservice-soap,webservice-rest,synchro-data-source,email-processing,custom-extension'), "sql"=>"origin", "default_value"=>"interactive", "is_null_allowed"=>true, "depends_on"=>array())));
 	}
diff --git a/core/dbproperty.class.inc.php b/core/dbproperty.class.inc.php
index 679861c5c..6be724cae 100644
--- a/core/dbproperty.class.inc.php
+++ b/core/dbproperty.class.inc.php
@@ -51,7 +51,7 @@ class DBProperty extends DBObject
 		MetaModel::Init_AddAttribute(new AttributeString("description", array("allowed_values"=>null, "sql"=>"description", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("value", array("allowed_values"=>null, "sql"=>"value", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 
-		MetaModel::Init_AddAttribute(new AttributeDateTime("change_date", array("allowed_values"=>null, "sql"=>"change_date", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeDateTime("change_date", array("allowed_values"=>null, "sql"=>"change_date", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("change_comment", array("allowed_values"=>null, "sql"=>"change_comment", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 	}
 
diff --git a/core/event.class.inc.php b/core/event.class.inc.php
index e24f64554..2c1e4ccf8 100644
--- a/core/event.class.inc.php
+++ b/core/event.class.inc.php
@@ -46,7 +46,7 @@ class Event extends DBObject implements iDisplay
 		MetaModel::Init_Params($aParams);
 		//MetaModel::Init_InheritAttributes();
 		MetaModel::Init_AddAttribute(new AttributeText("message", array("allowed_values"=>null, "sql"=>"message", "default_value"=>null, "is_null_allowed"=>false, "depends_on"=>array())));
-		MetaModel::Init_AddAttribute(new AttributeDateTime("date", array("allowed_values"=>null, "sql"=>"date", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeDateTime("date", array("allowed_values"=>null, "sql"=>"date", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("userinfo", array("allowed_values"=>null, "sql"=>"userinfo", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 //		MetaModel::Init_AddAttribute(new AttributeString("userinfo", array("allowed_values"=>null, "sql"=>"userinfo", "default_value"=>null, "is_null_allowed"=>true, "depends_on"=>array())));
 
diff --git a/datamodels/1.x/itop-attachments/datamodel.itop-attachments.xml b/datamodels/1.x/itop-attachments/datamodel.itop-attachments.xml
index 90c30af5b..afa70830e 100644
--- a/datamodels/1.x/itop-attachments/datamodel.itop-attachments.xml
+++ b/datamodels/1.x/itop-attachments/datamodel.itop-attachments.xml
@@ -53,7 +53,7 @@
         <field id="expire" xsi:type="AttributeDateTime">
           <sql>expire</sql>
           <default_value/>
-          <is_null_allowed>true</is_null_allowed>
+          <is_null_allowed>false</is_null_allowed>
         </field>
         <field id="temp_id" xsi:type="AttributeString">
           <sql>temp_id</sql>
diff --git a/datamodels/1.x/itop-tickets-1.0.0/datamodel.itop-tickets.xml b/datamodels/1.x/itop-tickets-1.0.0/datamodel.itop-tickets.xml
index 81bb8c7d7..c5309d821 100644
--- a/datamodels/1.x/itop-tickets-1.0.0/datamodel.itop-tickets.xml
+++ b/datamodels/1.x/itop-tickets-1.0.0/datamodel.itop-tickets.xml
@@ -54,7 +54,7 @@
         <field id="start_date" xsi:type="AttributeDateTime">
           <sql>start_date</sql>
           <default_value/>
-          <is_null_allowed>true</is_null_allowed>
+          <is_null_allowed>false</is_null_allowed>
         </field>
         <field id="document_list" xsi:type="AttributeLinkedSetIndirect">
           <linked_class>lnkTicketToDoc</linked_class>
diff --git a/datamodels/2.x/itop-attachments/datamodel.itop-attachments.xml b/datamodels/2.x/itop-attachments/datamodel.itop-attachments.xml
index c037c624a..da13c338b 100755
--- a/datamodels/2.x/itop-attachments/datamodel.itop-attachments.xml
+++ b/datamodels/2.x/itop-attachments/datamodel.itop-attachments.xml
@@ -58,7 +58,7 @@
         <field id="expire" xsi:type="AttributeDateTime">
           <sql>expire</sql>
           <default_value/>
-          <is_null_allowed>true</is_null_allowed>
+          <is_null_allowed>false</is_null_allowed>
         </field>
         <field id="temp_id" xsi:type="AttributeString">
           <sql>temp_id</sql>
diff --git a/synchro/synchrodatasource.class.inc.php b/synchro/synchrodatasource.class.inc.php
index e90f338f9..2bdd18709 100644
--- a/synchro/synchrodatasource.class.inc.php
+++ b/synchro/synchrodatasource.class.inc.php
@@ -1473,7 +1473,7 @@ class SynchroReplica extends DBObject implements iDisplay
 		MetaModel::Init_AddAttribute(new AttributeInteger("dest_id", array("allowed_values"=>null, "sql"=>"dest_id", "default_value"=>0, "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeClass("dest_class", array("class_category"=>"", "more_values"=>"", "sql"=>"dest_class", "default_value"=>'Organization', "is_null_allowed"=>true, "depends_on"=>array())));
 
-		MetaModel::Init_AddAttribute(new AttributeDateTime("status_last_seen", array("allowed_values"=>null, "sql"=>"status_last_seen", "default_value"=>"", "is_null_allowed"=>true, "depends_on"=>array())));
+		MetaModel::Init_AddAttribute(new AttributeDateTime("status_last_seen", array("allowed_values"=>null, "sql"=>"status_last_seen", "default_value"=>"", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeEnum("status", array("allowed_values"=>new ValueSetEnum('new,synchronized,modified,orphan,obsolete'), "sql"=>"status", "default_value"=>"new", "is_null_allowed"=>false, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeBoolean("status_dest_creator", array("allowed_values"=>null, "sql"=>"status_dest_creator", "default_value"=>0, "is_null_allowed"=>true, "depends_on"=>array())));
 		MetaModel::Init_AddAttribute(new AttributeString("status_last_error", array("allowed_values"=>null, "sql"=>"status_last_error", "default_value"=>'', "is_null_allowed"=>true, "depends_on"=>array())));