chore: major code cleanup and type safety using phpstan

src/Form/Service/Abstract/AbstractParticipantFieldHandler.php

@@ -130,7 +130,7 @@ abstract class AbstractParticipantFieldHandler implements ParticipantFieldHandle
      */
     protected function normalizeEmptyValue(mixed $value): mixed
     {
-        return empty($value) ? null : $value;
+        return $this->isEmptyValue($value) ? null : $value;
     }
 
     /**
@@ -146,13 +146,24 @@ abstract class AbstractParticipantFieldHandler implements ParticipantFieldHandle
      */
     protected function normalizeIntValue(mixed $value): ?int
     {
-        if (empty($value)) {
+        if ($this->isEmptyValue($value)) {
             return null;
         }
 
         return is_numeric($value) ? (int) $value : null;
     }
 
+    private function isEmptyValue(mixed $value): bool
+    {
+        return null === $value
+            || false === $value
+            || 0 === $value
+            || 0.0 === $value
+            || '' === $value
+            || '0' === $value
+            || [] === $value;
+    }
+
     /**
      * Normalizes a checkbox/form toggle value to a boolean.
      *