docs: @Nonnull
      public Person addPerson(Location location, @Nonnull String name, @Nullable String description) {
          if (getPersonWithName(name) == null) {
              Person person = new Person();
              person.setLocation(location);
              person.setName(name);
              person.setDescription(description);
  
              people.add(person);
  
              person.setId(idGenerator.generateId(person));
              addElementToInternalStructures(person);
  
              return person;
          } else {
              throw new IllegalArgumentException("A person named '" + name + "' already exists.");
          }
      }