diff --git a/lib/private/Collaboration/Collaborators/MailPlugin.php b/lib/private/Collaboration/Collaborators/MailPlugin.php
index 37ebf2fb129a0..770da77f26ab0 100644
--- a/lib/private/Collaboration/Collaborators/MailPlugin.php
+++ b/lib/private/Collaboration/Collaborators/MailPlugin.php
@@ -140,7 +140,7 @@ public function search($search, $limit, $offset, ISearchResult $searchResult): b
 						}
 						if ($exactEmailMatch && $this->shareeEnumerationFullMatch) {
 							try {
-								$cloud = $this->cloudIdManager->resolveCloudId($contact['CLOUD'][0]);
+								$cloud = $this->cloudIdManager->resolveCloudId($contact['CLOUD'][0] ?? '');
 							} catch (\InvalidArgumentException $e) {
 								continue;
 							}
@@ -165,7 +165,7 @@ public function search($search, $limit, $offset, ISearchResult $searchResult): b
 
 						if ($this->shareeEnumeration) {
 							try {
-								$cloud = $this->cloudIdManager->resolveCloudId($contact['CLOUD'][0]);
+								$cloud = $this->cloudIdManager->resolveCloudId($contact['CLOUD'][0] ?? '');
 							} catch (\InvalidArgumentException $e) {
 								continue;
 							}