code: public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
          return new MapStrLookup<>(map);
      }
docs: Returns a lookup which looks up values using a map.
  <p>
  If the map is null, then null will be returned from every lookup.
  The map result object is converted to a string using toString().
  
  @param <V> the type of the values supported by the lookup
  @param map  the map of keys to values, may be null
  @return a lookup using the map, not null