fix: type mismatches and handle nullable values

src/BusProNet/ResponseParser.php

@@ -31,12 +31,15 @@ class ResponseParser
     public function parseXmlString(string $type, string $content): mixed
     {
         $xml = simplexml_load_string($content);
+        if (false === $xml) {
+            throw new ResponseParserException('Unable to parse XML response');
+        }
 
         // Override type when present in XML to catch error responses
         $responseType = $type;
-        $responseTypeXml = $xml->xpath('satz/@typ');
+        $responseTypeXml = $xml->xpath('satz/@typ') ?: [];
         if (0 < count($responseTypeXml)) {
-            $responseType = (string) $xml->xpath('satz/@typ')[0];
+            $responseType = (string) $responseTypeXml[0];
         }
 
         switch ($responseType) {
@@ -91,7 +94,12 @@ class ResponseParser
         $gender = 'W' === strtoupper($gender) ? 'F' : strtoupper($gender);
 
         $dateString = (string) $addressXml->geburtsdatum;
-        $dateOfBirth = empty($dateString) ? null : \DateTimeImmutable::createFromFormat('d.m.Y', $dateString);
+        $dateOfBirth = null;
+
+        if ('' !== $dateString) {
+            $parsedDate = \DateTimeImmutable::createFromFormat('d.m.Y', $dateString);
+            $dateOfBirth = false === $parsedDate ? null : $parsedDate;
+        }
 
         $response = new ProfileResponse();
         $response
@@ -146,7 +154,7 @@ class ResponseParser
         $personId = (int) $xml->idperson;
 
         $updated = false;
-        $updatedXml = $xml->xpath('änderung|aenderung');
+        $updatedXml = $xml->xpath('änderung|aenderung') ?: [];
         if (0 < count($updatedXml)) {
             $updated = 'true' === strtolower((string) $updatedXml[0]);
         }