Fix market card save validation

public/api/market-occurrence.php

@@ -33,6 +33,7 @@ if ($requestMethod === 'POST') {
         echo json_encode(['ok' => false, 'error' => 'Ungültige Anfrage']);
         exit;
     }
+    try {
         $scope = (string) ($payload['scope'] ?? '');
         $id = market_management_require_positive_id($payload['id'] ?? null, 'id');
         $fields = is_array($payload['fields'] ?? null) ? $payload['fields'] : [];
@@ -61,13 +62,17 @@ if ($requestMethod === 'POST') {
             market_management_update_market($pdo, (int) ($existingOccurrence['market_definition_id'] ?? 0), $marketFields);
         }
         if ($contactFields !== []) {
-            $contactId = (int) ($fields['contact_person_id'] ?? $existingOccurrence['contact_person_id'] ?? 0);
+            $submittedContactId = trim((string) ($fields['contact_person_id'] ?? ''));
+            $contactId = (int) ($submittedContactId !== '' ? $submittedContactId : ($existingOccurrence['contact_person_id'] ?? 0));
             update_contact_details($pdo, $contactId, $contactFields);
         }
         $organizerFields = [];
         foreach (['organization_contact_id', 'contact_person_id'] as $organizerField) {
             if (array_key_exists($organizerField, $fields)) {
-                $organizerFields[$organizerField] = $fields[$organizerField];
+                $value = trim((string) $fields[$organizerField]);
+                if ($value !== '') {
+                    $organizerFields[$organizerField] = $value;
+                }
                 unset($fields[$organizerField]);
             }
         }
@@ -87,6 +92,11 @@ if ($requestMethod === 'POST') {
         }
         echo json_encode(['ok' => true]);
         exit;
+    } catch (Throwable $error) {
+        http_response_code(422);
+        echo json_encode(['ok' => false, 'error' => $error->getMessage()], JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
+        exit;
+    }
 }
 
 $occurrenceId = filter_input(INPUT_GET, 'id', FILTER_VALIDATE_INT);