[BUGFIX] Fix remaining function call

Classes/Controller/MailController.php

@@ -204,9 +204,9 @@ class MailController extends ActionController {
 		$selectedExtension, $selectedTemplate, $selectedLanguage, $selectedContent, $selectedSubject
 	) {
 		/** @var Template $template */
-		$template = $this->templateRepository->findTemplate(
+		$template = $this->templateRepository->findOneByTemplate(
 			$selectedExtension, $selectedTemplate, $selectedLanguage
-		)->getFirst();
+		);
 
 		$templateAlreadyExists = TRUE;
 		$objectManager = GeneralUtility::makeInstance(ObjectManager::class);