N°6974 - Flatten classes in datamodel (#603)

* N°6974 - Flatten classes in datamodel

* N°6882 - LoadDelta() in lax/strict mode

* N°6974 - Flatten classes in datamodel

* N°6882 - LoadDelta() in lax/strict mode

* N°7186 - Code hardening

* N°6974 - Flatten classes in datamodel

* N°6660 and N°7318 - Support delete_if_exists and define_if_not_exists in XML injection

* N°6974 - Flatten classes in datamodel

* Apply suggestions from code review

* Update core/designdocument.class.inc.php

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Co-authored-by: Molkobain <lajarige.guillaume@free.fr>

setup/itopdesignformat.class.inc.php

@@ -895,7 +895,9 @@ class iTopDesignFormat
 			// N°6562 textContent is readonly, see https://www.php.net/manual/en/class.domnode.php#95545
 			// $oNode->textContent = '';
 			// N°6562 to update text node content we must use the node methods !
-			$oNode->removeChild($oNode->firstChild);
+			if ($oNode->firstChild) {
+				$oNode->removeChild($oNode->firstChild);
+			}
 			$oCodeNode = $oNode->ownerDocument->createElement("code", $sCode);
 			$oNode->appendChild($oCodeNode);
 		}