code: @Test public void should_extract_single_value_from_maps_by_key(){
    String key1="key1";
    String key2="key2";
    Map<String,Employee> map1=new HashMap<>();
    map1.put(key1,yoda);
    Employee luke=new Employee(2L,new Name("Luke"),22);
    map1.put(key2,luke);
    Map<String,Employee> map2=new HashMap<>();
    map2.put(key1,yoda);
    Employee han=new Employee(3L,new Name("Han"),31);
    map2.put(key2,han);
    List<Map<String,Employee>> maps=asList(map1,map2);
    assertThat(maps).extracting(key2).containsExactly(luke,han);
    assertThat(maps).extracting(key2,Employee.class).containsExactly(luke,han);
    assertThat(maps).extracting(key1).containsExactly(yoda,yoda);
    assertThat(maps).extracting("bad key").containsExactly(null,null);
  }
  