handle (empty) phone elements

Author: mathielen

src/CXml/Model/Phone.php

@@ -36,7 +36,7 @@ public function getTelephoneNumberAsString(): ?string
         $telephoneNumber = $this->telephoneNumber->getNumber();
         $extension = null === $this->telephoneNumber->getExtension() ? '' : ' -' . $this->telephoneNumber->getExtension();
 
-        if ($telephoneNumber === '') {
+        if ('' === $telephoneNumber) {
             return null;
         }