code: public static <K, V> Function<K, V> forMap(Map<K, V> map) {
      return new FunctionForMapNoDefault<K, V>(map);
    }
docs: Returns a function which performs a map lookup. The returned function throws an {@link
  IllegalArgumentException} if given a key that does not exist in the map. See also {@link
  #forMap(Map, Object)}, which returns a default value in this case.
  
  <p>Note: if {@code map} is a {@link com.google.common.collect.BiMap BiMap} (or can be one), you
  can use {@link com.google.common.collect.Maps#asConverter Maps.asConverter} instead to get a
  function that also supports reverse conversion.