Add missing annotation (#136)

*Add missing nullable annotation for calls in kotlin

Author: Fabtron

core/src/main/java/io/snabble/sdk/auth/TokenRegistry.java

@@ -51,6 +51,7 @@ public void invalidate() {
         tokens.clear();
     }
 
+    @Nullable
     private synchronized Token refreshToken(Project project, boolean isRetry) {
         if (totp == null) {
             return null;
@@ -162,19 +163,16 @@ private long getOffsetTime() {
      * <p>
      * Returns null if not valid token could be generated. (invalid secret, timeouts, no connection)
      */
-    public synchronized Token getToken(Project project) {
+    @Nullable
+    public synchronized Token getToken(@Nullable Project project) {
         if (project == null) {
             return null;
         }
 
         Token token = tokens.get(project.getId());
 
         if (token != null) {
-            long tokenInterval = (token.expiresAt - token.issuedAt);
-            long invalidAt = token.issuedAt + tokenInterval / 2;
-
-            long seconds = getOffsetTime();
-            if (seconds >= invalidAt) {
+            if (isValid(token)) {
                 Logger.d("Token timed out, requesting new token");
                 Token newToken = refreshToken(project, false);
                 if (newToken != null) {
@@ -190,20 +188,6 @@ public synchronized Token getToken(Project project) {
         return token;
     }
 
-    /**
-     * Returns the locally stored token or null if invalid
-     */
-    @Nullable
-    public Token getLocalToken(@NonNull final Project project) {
-        final Token token = tokens.get(project.getId());
-
-        if (isValid(token)) {
-            return token;
-        } else {
-            return null;
-        }
-    }
-
     @NonNull
     private Boolean isValid(@Nullable final Token token) {
         if (token == null) return false;