Return the score of the specified element of the sorted set at key. If the specified element
does not exist in the sorted set, or the key does not exist at all, a special 'nil' value is
returned.
<p>
<b>Time complexity:</b> O(1)
@param key
@param member
@return the score
Return the score of the specified element of the sorted set at key. If the specified element does not exist in the sorted set, or the key does not exist at all, a special 'nil' value is returned. <p> <b>Time complexity:</b> O(1) @param key @param member @return the score