fix normalization for null accompanying period docgen

src/Bundle/ChillPersonBundle/Serializer/Normalizer/AccompanyingPeriodDocGenNormalizer.php

@@ -44,6 +44,7 @@ class AccompanyingPeriodDocGenNormalizer implements ContextAwareNormalizerInterf
     private const PERIOD_NULL = [
         'id',
         'closingDate' => DateTime::class,
+        'closingMotive' => AccompanyingPeriod\ClosingMotive::class,
         'confidential',
         'confidentialText',
         'createdAt' => DateTime::class,