adding missing email address for principal

* fix #8515
* add mail only if it exists

lib/private/connector/sabre/principal.php

@@ -26,11 +26,17 @@ class OC_Connector_Sabre_Principal implements \Sabre\DAVACL\PrincipalBackend\Bac
 
 		if ($prefixPath == 'principals') {
 			foreach(OC_User::getUsers() as $user) {
+
 				$user_uri = 'principals/'.$user;
 				$principals[] = array(
 					'uri' => $user_uri,
 					'{DAV:}displayname' => $user,
 				);
+
+				$email= \OCP\Config::getUserValue($user, 'settings', 'email');
+				if($email) {
+					$principals['{http://sabredav.org/ns}email-address'] = $email;
+				}
 			}
 		}
 
@@ -49,10 +55,16 @@ class OC_Connector_Sabre_Principal implements \Sabre\DAVACL\PrincipalBackend\Bac
 		list($prefix, $name) = explode('/', $path);
 
 		if ($prefix == 'principals' && OC_User::userExists($name)) {
+
 			return array(
 				'uri' => 'principals/'.$name,
 				'{DAV:}displayname' => $name,
 			);
+
+			$email= \OCP\Config::getUserValue($user, 'settings', 'email');
+			if($email) {
+				$principals['{http://sabredav.org/ns}email-address'] = $email;
+			}
 		}
 
 		return null;