diff --git a/lam/templates/tools/multiEdit.php b/lam/templates/tools/multiEdit.php
index 9ab83c01f..d27ad7182 100644
--- a/lam/templates/tools/multiEdit.php
+++ b/lam/templates/tools/multiEdit.php
@@ -476,16 +476,18 @@ function dryRun(): array {
 	// store LDIF
 	$filename = 'ldif' . getRandomNumber() . '.ldif';
 	$out = @fopen(dirname(__FILE__) . '/../../tmp/' . $filename, "wb");
-	fwrite($out, $ldif);
-	$container->addElement(new htmlOutputText(_('LDIF file')), true);
-	$ldifLink = new htmlLink($filename, '../../tmp/' . $filename);
-	$ldifLink->setTargetWindow('_blank');
-	$container->addElement($ldifLink, true);
-	$container->addVerticalSpace('20px');
-	$container->addElement(new htmlOutputText(_('Log output')), true);
-	$container->addElement(new htmlInputTextarea('log', $log, 100, 30), true);
-	// generate HTML
-	fclose ($out);
+	if ($out !== false) {
+		fwrite($out, $ldif);
+		$container->addElement(new htmlOutputText(_('LDIF file')), true);
+		$ldifLink = new htmlLink($filename, '../../tmp/' . $filename);
+		$ldifLink->setTargetWindow('_blank');
+		$container->addElement($ldifLink, true);
+		$container->addVerticalSpace('20px');
+		$container->addElement(new htmlOutputText(_('Log output')), true);
+		$container->addElement(new htmlInputTextarea('log', $log, 100, 30), true);
+		// generate HTML
+		fclose ($out);
+	}
 	ob_start();
 	$tabindex = 1;
 	parseHtml(null, $container, array(), true, $tabindex, 'user');
@@ -587,13 +589,16 @@ function doModify(): array {
  * Returns the HTML code for a htmlStatusMessage
  *
  * @param htmlStatusMessage $msg message
- * @return String HTML code
+ * @return string HTML code
  */
-function getMessageHTML($msg) {
+function getMessageHTML(htmlStatusMessage $msg): string {
 	$tabindex = 0;
 	ob_start();
 	parseHtml(null, $msg, array(), true, $tabindex, 'user');
 	$content = ob_get_contents();
 	ob_end_clean();
+	if ($content === false) {
+		return '';
+	}
 	return $content;
 }
diff --git a/lam/templates/tools/ou_edit.php b/lam/templates/tools/ou_edit.php
index 733624f7d..79714adcc 100644
--- a/lam/templates/tools/ou_edit.php
+++ b/lam/templates/tools/ou_edit.php
@@ -14,7 +14,7 @@ use \htmlGroup;
 /*
 
   This code is part of LDAP Account Manager (http://www.ldap-account-manager.org/)
-  Copyright (C) 2003 - 2021  Roland Gruber
+  Copyright (C) 2003 - 2022  Roland Gruber
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -115,38 +115,43 @@ if (isset($_POST['createOU']) || isset($_POST['deleteOU'])) {
 	elseif (isset($_POST['deleteOU'])) {
 		// check for sub entries
 		$sr = ldap_list($_SESSION['ldap']->server(), $_POST['deleteableOU'], "ObjectClass=*", array(""));
-		$info = ldap_get_entries($_SESSION['ldap']->server(), $sr);
-		if ($sr && ($info['count'] === 0)) {
-			// print header
-			include '../../lib/adminHeader.inc';
-			echo '<div class="smallPaddingContent">';
-			echo "<form action=\"ou_edit.php\" method=\"post\">\n";
-			$tabindex = 1;
-			$container = new htmlResponsiveRow();
-			$label = new htmlOutputText(_("Do you really want to delete this OU?"));
-			$label->colspan = 5;
-			$container->add($label, 12);
-			$container->addVerticalSpacer('1rem');
-			$dnLabel = new htmlOutputText(getAbstractDN($_POST['deleteableOU']));
-			$dnLabel->colspan = 5;
-			$container->add($dnLabel, 12);
-			$container->addVerticalSpacer('1rem');
-			$buttonGroup = new htmlGroup();
-			$buttonGroup->addElement(new htmlButton('sure', _("Delete")));
-			$buttonGroup->addElement(new htmlSpacer('0.5rem', null));
-			$buttonGroup->addElement(new htmlButton('abort', _("Cancel")));
-			$container->add($buttonGroup, 12);
-			$container->add(new htmlHiddenInput('deleteOU', 'submit'), 12);
-			$container->add(new htmlHiddenInput('deletename', $_POST['deleteableOU']), 12);
-			addSecurityTokenToMetaHTML($container);
-			parseHtml(null, $container, array(), false, $tabindex, 'user');
-			echo "</form>";
-			echo '</div>';
-			include '../../lib/adminFooter.inc';
-			exit();
+		if ($sr === false) {
+			$error = _("OU is not empty or invalid!");
 		}
 		else {
-			$error = _("OU is not empty or invalid!");
+			$info = ldap_get_entries($_SESSION['ldap']->server(), $sr);
+			if (($info !== false) && ($info['count'] === 0)) {
+				// print header
+				include '../../lib/adminHeader.inc';
+				echo '<div class="smallPaddingContent">';
+				echo "<form action=\"ou_edit.php\" method=\"post\">\n";
+				$tabindex = 1;
+				$container = new htmlResponsiveRow();
+				$label = new htmlOutputText(_("Do you really want to delete this OU?"));
+				$label->colspan = 5;
+				$container->add($label, 12);
+				$container->addVerticalSpacer('1rem');
+				$dnLabel = new htmlOutputText(getAbstractDN($_POST['deleteableOU']));
+				$dnLabel->colspan = 5;
+				$container->add($dnLabel, 12);
+				$container->addVerticalSpacer('1rem');
+				$buttonGroup = new htmlGroup();
+				$buttonGroup->addElement(new htmlButton('sure', _("Delete")));
+				$buttonGroup->addElement(new htmlSpacer('0.5rem', null));
+				$buttonGroup->addElement(new htmlButton('abort', _("Cancel")));
+				$container->add($buttonGroup, 12);
+				$container->add(new htmlHiddenInput('deleteOU', 'submit'), 12);
+				$container->add(new htmlHiddenInput('deletename', $_POST['deleteableOU']), 12);
+				addSecurityTokenToMetaHTML($container);
+				parseHtml(null, $container, array(), false, $tabindex, 'user');
+				echo "</form>";
+				echo '</div>';
+				include '../../lib/adminFooter.inc';
+				exit();
+			}
+			else {
+				$error = _("OU is not empty or invalid!");
+			}
 		}
 	}
 }
diff --git a/lam/templates/tools/treeView.php b/lam/templates/tools/treeView.php
index f275995a5..59d7246c4 100644
--- a/lam/templates/tools/treeView.php
+++ b/lam/templates/tools/treeView.php
@@ -75,11 +75,13 @@ function showTree(): void {
 			if ((strlen($initialDn) > strlen($rootDn)) && substr($initialDn, -1 * strlen($rootDn)) === $rootDn) {
 				$extraDnPart = substr($initialDn, 0, (-1 * strlen($rootDn)) - 1);
 				$dnParts = ldap_explode_dn($extraDnPart, 0);
-				unset($dnParts['count']);
-				$dnPartsCount = sizeof($dnParts);
-				for ($i = 0; $i < $dnPartsCount; $i++) {
-					$currentParts = array_slice($dnParts, $dnPartsCount - ($i + 1));
-					$openInitial[] = '"' . base64_encode(implode(',', $currentParts) . ',' . $rootDn) . '"';
+				if ($dnParts !== false) {
+					unset($dnParts['count']);
+					$dnPartsCount = sizeof($dnParts);
+					for ($i = 0; $i < $dnPartsCount; $i++) {
+						$currentParts = array_slice($dnParts, $dnPartsCount - ($i + 1));
+						$openInitial[] = '"' . base64_encode(implode(',', $currentParts) . ',' . $rootDn) . '"';
+					}
 				}
 			}
 		}
diff --git a/lam/templates/upload/massBuildAccounts.php b/lam/templates/upload/massBuildAccounts.php
index 64f77026d..06efc8668 100644
--- a/lam/templates/upload/massBuildAccounts.php
+++ b/lam/templates/upload/massBuildAccounts.php
@@ -126,13 +126,16 @@ if ($_FILES['inputfile'] && ($_FILES['inputfile']['size'] > 0)) {
 	$uploadColumns = getUploadColumns($type, $selectedModules);
 	// read input file
 	$handle = fopen ($_FILES['inputfile']['tmp_name'], "r");
-	if (($head = fgetcsv($handle, 2000)) !== false ) { // head row
-		foreach ($head as $i => $headItem) {
-			$ids[$headItem] = $i;
+	if ($handle !== false) {
+		if (($head = fgetcsv($handle, 2000)) !== false ) { // head row
+			foreach ($head as $i => $headItem) {
+				$ids[$headItem] = $i;
+			}
 		}
-	}
-	while (($line = fgetcsv($handle, 2000)) !== false ) { // account rows
-		$data[] = $line;
+		while (($line = fgetcsv($handle, 2000)) !== false ) { // account rows
+			$data[] = $line;
+		}
+		fclose($handle);
 	}
 
 	$errors = array();
diff --git a/phpstan.neon b/phpstan.neon
index 6de3dbc88..067235067 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -28,3 +28,6 @@ parameters:
 		- '#Cannot assign new offset to array<int, string>\|string.#'
 		- '#Parameter \#1 \$result of function ldap_free_result expects LDAP\\Result, array\|LDAP\\Result given.#'
 		- '#Cannot access offset .* on array\|int.#'
+		- '#Parameter \#1 \$haystack of function strpos expects string, int\|string given.#'
+		- '#Argument of an invalid type array\|int supplied for foreach, only iterables are supported.#'
+		- '#Cannot access offset mixed on non-empty-array\|int.#'