Now SORT returns an empty bulk reply if the key does not exist

redis.c

@@ -4839,7 +4839,7 @@ static void sortCommand(redisClient *c) {
     /* Lookup the key to sort. It must be of the right types */
     sortval = lookupKeyRead(c->db,c->argv[1]);
     if (sortval == NULL) {
-        addReply(c,shared.nokeyerr);
+        addReply(c,shared.nullmultibulk);
         return;
     }
     if (sortval->type != REDIS_SET && sortval->type != REDIS_LIST &&

test-redis.tcl

@@ -962,6 +962,10 @@ proc main {server port} {
         $r sort mylist BY weight_* GET #
     } {2 1 3}
 
+    test {SORT with constant GET} {
+        $r sort mylist GET foo
+    } {{} {} {}}
+
     test {LREM, remove all the occurrences} {
         $r flushdb
         $r rpush mylist foo