fix: fixed UserManagerTest

Server/src/test/java/uulm/teamname/marvelous/server/netconnector/UserManagerTest.java

@@ -24,7 +24,7 @@ class UserManagerTest {
     void beforeEach() {
         connection = mock(WebSocket.class);
         // when(connection.hashCode()).thenReturn(1); // just for testing, of course
-        manager = spy(new UserManager(new JSON(null))); // FIXME: This shouldn't be null, of course
+        manager = spy(new UserManager()); // FIXME: This shouldn't be null, of course
 
         handshake = mock(ClientHandshake.class);
         when(handshake.getResourceDescriptor()).thenReturn("/someDescriptor");