diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8094647ca..f523db0af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@
 - Fix locked SQLite database for the CLI tools (#8035)
 - Fix importing contacts with no email address (#8227)
 - Fix so session's search scope is not used if search is not active (#8199)
+- Fix some PHP8 warnings (#8239)
 
 ## Release 1.5.0
 
diff --git a/program/include/rcmail_attachment_handler.php b/program/include/rcmail_attachment_handler.php
index b37f1fe64..2ee02e07f 100644
--- a/program/include/rcmail_attachment_handler.php
+++ b/program/include/rcmail_attachment_handler.php
@@ -229,7 +229,7 @@ class rcmail_attachment_handler
                 }
             }
             else {
-                $data = $attachment['data'];
+                $data = $attachment['data'] ?? '';
                 if (!$data && $attachment['path']) {
                     $data = file_get_contents($attachment['path']);
                 }
diff --git a/program/lib/Roundcube/rcube_addressbook.php b/program/lib/Roundcube/rcube_addressbook.php
index 571e815f5..463d46f8b 100644
--- a/program/lib/Roundcube/rcube_addressbook.php
+++ b/program/lib/Roundcube/rcube_addressbook.php
@@ -685,20 +685,34 @@ abstract class rcube_addressbook
         static $compose_mode;
 
         if (!isset($compose_mode)) {
-            $compose_mode = rcube::get_instance()->config->get('addressbook_name_listing', 0);
+            $compose_mode = (int) rcube::get_instance()->config->get('addressbook_name_listing', 0);
         }
 
+        $get_names = function ($contact, $fields) {
+            $result = [];
+            foreach ($fields as $field) {
+                if (!empty($contact[$field])) {
+                    $result[] = $contact[$field];
+                }
+            }
+            return $result;
+        };
+
         switch ($compose_mode) {
         case 3:
-            $fn = implode(' ', [$contact['surname'] . ',', $contact['firstname'], $contact['middlename']]);
+            $names = $get_names($contact, ['firstname', 'middlename']);
+            if (!empty($contact['surname'])) {
+                array_unshift($names, $contact['surname'] . ',');
+            }
+            $fn = implode(' ', $names);
             break;
         case 2:
             $keys = ['surname', 'firstname', 'middlename'];
-            $fn   = implode(' ', array_filter(array_intersect_key($contact, array_flip($keys))));
+            $fn   = implode(' ', $get_names($contact, $keys));
             break;
         case 1:
             $keys = ['firstname', 'middlename', 'surname'];
-            $fn   = implode(' ', array_filter(array_intersect_key($contact, array_flip($keys))));
+            $fn   = implode(' ', $get_names($contact, $keys));
             break;
         case 0:
             if (!empty($contact['name'])) {
@@ -706,7 +720,7 @@ abstract class rcube_addressbook
             }
             else {
                 $keys = ['prefix', 'firstname', 'middlename', 'surname', 'suffix'];
-                $fn   = implode(' ', array_filter(array_intersect_key($contact, array_flip($keys))));
+                $fn   = implode(' ', $get_names($contact, $keys));
             }
             break;
         default:
diff --git a/program/lib/Roundcube/rcube_mime.php b/program/lib/Roundcube/rcube_mime.php
index d56da5651..ca5bfa66d 100644
--- a/program/lib/Roundcube/rcube_mime.php
+++ b/program/lib/Roundcube/rcube_mime.php
@@ -494,7 +494,9 @@ class rcube_mime
                 // remove quote chars
                 $line = substr($line, $q);
                 // remove (optional) space-staffing
-                if ($line[0] === ' ') $line = substr($line, 1);
+                if (isset($line[0]) && $line[0] === ' ') {
+                    $line = substr($line, 1);
+                }
 
                 // The same paragraph (We join current line with the previous one) when:
                 // - the same level of quoting
diff --git a/tests/Framework/Addressbook.php b/tests/Framework/Addressbook.php
index d0a44f989..73116c3e5 100644
--- a/tests/Framework/Addressbook.php
+++ b/tests/Framework/Addressbook.php
@@ -27,4 +27,66 @@ class Framework_Addressbook extends PHPUnit\Framework\TestCase
 
         $this->assertSame(['home' => ['test@test.com']], $result);
     }
+
+    /**
+     * Test for compose_list_name() method
+     */
+    function test_compose_list_name()
+    {
+        $contact = [];
+        $result  = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('', $result);
+
+        $contact = ['email' => 'email@address.tld'];
+        $result  = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('email@address.tld', $result);
+
+        $contact = ['email' => 'email@address.tld', 'organization' => 'Org'];
+        $result  = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('Org', $result);
+
+        $contact['firstname'] = 'First';
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('First', $result);
+
+        $contact['surname'] = 'Last';
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('First Last', $result);
+
+        $contact['name'] = 'Name';
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('Name', $result);
+
+        unset($contact['name']);
+        $contact['prefix'] = 'Dr.';
+        $contact['suffix'] = 'Jr.';
+        $contact['middlename'] = 'M.';
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('Dr. First M. Last Jr.', $result);
+
+        // TODO: Test different modes
+        /*
+        rcube::get_instance()->config->set('addressbook_name_listing', 3);
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('Last, First M.', $result);
+
+        rcube::get_instance()->config->set('addressbook_name_listing', 2);
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('Last First M.', $result);
+
+        rcube::get_instance()->config->set('addressbook_name_listing', 1);
+        $result = rcube_addressbook::compose_list_name($contact);
+
+        $this->assertSame('First M. Last', $result);
+        */
+    }
 }