LLEN
Syntax
        LLEN key
- Available since:
 - 1.0.0
 - Time complexity:
 - O(1)
 - ACL categories:
 - 
              
                
@read,@list,@fast, 
Returns the length of the list stored at key.
If key does not exist, it is interpreted as an empty list and 0 is returned.
An error is returned when the value stored at key is not a list.