code: public void addProperty(final String propertyName, final Collection<String> values) {
          Preconditions.checkNotNull(values);
          Preconditions.checkNotNull(propertyName);
          List<String> list = properties.get(propertyName);
          if (list == null) {
              properties.put(propertyName, new ArrayList<>(values));
          } else {
              list.addAll(values);
          }
      }
docs: Add a list of value to a property on this bean.
  
  @param propertyName name of the property as defined by the bean's schema.
  @param values final String representations of the parameterized type of the collection
  that conforms to its type as defined by the bean's schema.