Fix null reference error in EmailTemplatePreview

- Add conditional rendering for previewTemplate to prevent null reference
- Add null checks in EmailTemplatePreview component for template properties
- Fix shortcodes filtering to handle null template properties
- Remove non-null assertion operator and use proper conditional rendering

Fixes: "Cannot read properties of null (reading 'email_subject')" error

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/components/admin/EmailTemplatePreview.tsx

@@ -47,8 +47,10 @@ export function EmailTemplatePreview({
 
   // Generate preview with dummy shortcode data
   const generatePreview = () => {
-    const processedSubject = ShortcodeProcessor.process(template.email_subject);
-    const processedContent = ShortcodeProcessor.process(template.email_body_html);
+    if (!template) return '<div>No template selected</div>';
+
+    const processedSubject = ShortcodeProcessor.process(template.email_subject || '');
+    const processedContent = ShortcodeProcessor.process(template.email_body_html || '');
 
     if (previewMode === 'master') {
       const fullHtml = EmailTemplateRenderer.render({
@@ -190,7 +192,8 @@ export function EmailTemplatePreview({
               {['{nama}', '{email}', '{order_id}', '{tanggal_pesanan}', '{total}', '{metode_pembayaran}',
                '{produk}', '{link_akses}', '{tanggal_konsultasi}', '{jam_konsultasi}', '{link_meet}',
                '{judul_event}', '{tanggal_event}', '{jam_event}', '{link_event}'].filter(shortcode =>
-                 template.email_subject.includes(shortcode) || template.email_body_html.includes(shortcode)
+                 (template.email_subject && template.email_subject.includes(shortcode)) ||
+                 (template.email_body_html && template.email_body_html.includes(shortcode))
               ).map(shortcode => (
                 <code key={shortcode} className="bg-blue-100 px-2 py-1 rounded text-xs">
                   {shortcode}

src/components/admin/settings/NotifikasiTab.tsx

@@ -679,13 +679,15 @@ export function NotifikasiTab() {
       </Card>
 
       {/* Modal Email Preview */}
+      {previewTemplate && (
         <EmailTemplatePreview
-        template={previewTemplate!}
+          template={previewTemplate}
           open={isPreviewOpen}
           onClose={() => setIsPreviewOpen(false)}
           onTest={sendTestEmail}
-        isTestSending={testingTemplate === previewTemplate?.id}
+          isTestSending={testingTemplate === previewTemplate.id}
         />
+      )}
     </div>
   );
 }