Merge pull request #1520 from ropalka/UNDERTOW-2316

[UNDERTOW-2316] Unify InMemorySessionManager with DistributableSessionManager - allow null exchanges

Author: fl4via

core/src/main/java/io/undertow/server/session/InMemorySessionManager.java

@@ -228,15 +228,18 @@ private String createAndSaveNewID(SessionImpl session) {
     public Session getSession(final HttpServerExchange serverExchange, final SessionConfig config) {
         if (serverExchange != null) {
             SessionImpl newSession = serverExchange.getAttachment(NEW_SESSION);
-            if(newSession != null) {
+            if (newSession != null) {
                 return newSession;
             }
-        } else {
-            return null;
         }
+
+        if (config == null) {
+            throw UndertowMessages.MESSAGES.couldNotFindSessionCookieConfig();
+        }
+
         String sessionId = config.findSessionId(serverExchange);
         InMemorySessionManager.SessionImpl session = (SessionImpl) getSession(sessionId);
-        if(session != null && serverExchange != null) {
+        if (session != null && serverExchange != null) {
             session.requestStarted(serverExchange);
         }
         return session;