A valid user session is required for circles.

The circles app depends on a valid userId. A public shared calender might be viewed by guests without a user session. For such requests the principal is null.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

apps/dav/lib/Connector/Sabre/Principal.php

@@ -178,8 +178,10 @@ class Principal implements BackendInterface {
 				return $this->userToPrincipal($user);
 			}
 		} elseif ($prefix === 'principals/circles') {
+			if ($this->userSession->getUser() !== null) {
 				return $this->circleToPrincipal($name);
 			}
+		}
 		return null;
 	}