Fix psalm issues related to the user backend

- Reflect the actual return value returned by the implementation in the
  the interface. E.g. IUser|bool -> IUser|false
- Remove $hasLoggedIn parameter from private countUser implementation.
  Replace the two call with the equivalent countSeenUser
- getBackend is nuallable, add this to the interface
- Use backend interface to make psalm happy about call to undefined
  methods. Also helps with getting rid at some point of the old
  implementActions

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

1 files changed, 1 insertions, 2 deletions

diff --git a/lib/public/IUser.php b/lib/public/IUser.php
index 1a1d1e44d8a..ce9cf0096ec 100644
--- a/lib/public/IUser.php
+++ b/lib/public/IUser.php
@@ -113,10 +113,9 @@ interface IUser {
 	/**
 	 * Get the backend for the current user object
 	 *
-	 * @return UserInterface
 	 * @since 15.0.0
 	 */
-	public function getBackend();
+	public function getBackend(): ?UserInterface;
 
 	/**
 	 * check if the backend allows the user to change his avatar on Personal page