Returns a key-value mapping associated with the least key
strictly greater than the given key, or {@code null} if there
is no such key.
@param key the key
@return an entry with the least key greater than {@code key},
or {@code null} if there is no such key
@throws ClassCastException if the specified key cannot be compared
with the keys currently in the map
@throws NullPointerException if the specified key is null
and this map does not permit null keys
Returns a key-value mapping associated with the least key strictly greater than the given key, or {@code null} if there is no such key.
@param key the key @return an entry with the least key greater than {@code key}, or {@code null} if there is no such key @throws ClassCastException if the specified key cannot be compared with the keys currently in the map @throws NullPointerException if the specified key is null and this map does not permit null keys