g. updating a
        // customer, where there is no persistent card parameter.  Mark those values
        // which don't persist as transient
        if ($partial) {
            $removed = new Util\Set();
        } else {
            $removed = new Util\Set(array_diff(array_keys($this->_values), array_keys($values)));
        }

        foreach ($removed->toArray() as $k) {
            unset($this->$k);
        }

        $this->updateAttributes($values, $opts, false);
        foreach ($values as $k => $v) {
            $this->_transientValues->discard($k);
            $this->_unsavedValues->discard($k);
        }
    }

    /**
     * Mass assigns attributes on the model.
     *
     * @param array $values
     * @param null|string|array|Util\RequestOptions $opts
     * @param boolean $dirty Defaults to true.
     */
    public function updateAttributes($values, $opts = null, $dirty = true)
    {
        foreach ($values as $k => $v) {
            // Special-case metadata to always be cast as a StripeObject
            // This is necessary in case metadata is empty, as PHP arrays do
            // not differentiate between lists and hashes, and we consider
            // empty arrays to be lists.
            if ($k === "metadata") {
                $this->_values[$k] = StripeObject::constructFrom($v, $opts);
            } else {
                $this->_values[$k] = Util\Util::convertToStripeObject($v, $opts);
            }
            if ($dirty) {
                $this->dirtyValue($this->_values[$k]);
            }
            $this->_unsavedValues->add($k);
        }
    }

    /**
     * @return array A recursive mapping of attributes to values for this object,
     *    including the proper value for deleted attributes.
     */
    public function serializeParameters($force = false)
    {
        $updateParams = [];

        foreach ($this->_values as $k => $v) {
            // There are a few reasons that we may want to add in a parameter for
            // update:
            //
            //   1. The `$force` option has been set.
            //   2. We know that it was modified.
            //   3. Its value is a StripeObject. A StripeObject may contain modified
            //      values within in that its parent StripeObject doesn't know about.
            //
            $original = array_key_exists($k, $this->_originalValues) ? $this->_originalValues[$k] : null;
            $unsaved = $this->_unsavedValues->includes($k);
            if ($force || $unsaved || $v instanceof StripeObject) {
                $updateParams[$k] = $this->serializeParamsValue(
                    $this->_values[$k],
                    $original,
                    $unsaved,
                    $force,
                    $k
                );
            }
        }

        // a `null` that makes it out of `serializeParamsValue` signals an empty
        // value that we shouldn't appear in the serialized form of the object
        $updateParams = array_filter(
            $updateParams,
            function ($v) {
                return $v !== null;
            }
        );

        return $updateParams;
    }


    public function serializeParamsValue($value, $original, $unsaved, $force, $key = null)
    {
        // The logic here is that essentially any object embedded in another
        // object that had a `type` is actually an API resource of a different
        // type that's been included in the response. These other resources must
        // be updated from their proper endpoints, and therefore they are not
        // included when serializing even if they've been modified.
        //
        // There are _some_ known exceptions though.
        //
        // For example, if the value is unsaved (meaning the user has set it), and
        // it looks like the API resource is persisted with an ID, then we include
        // the object so that parameters are serialized with a reference to its
        // ID.
        //
        // Another example is that on save API calls it's sometimes desirable to
        // update a customer's default source by setting a new card (or other)
        // object with `->source=` and then saving the customer. The
        // `saveWithParent` flag to override the default behavior allows us to
        // handle these exceptions.
        //
        // We throw an error if a property was set explicitly but we can't do
        // anything with it because the integration is probably not working as the
        // user intended it to.
        if ($value === null) {
            return "";
        } elseif (($value instanceof APIResource) && (!$value->saveWithParent)) {
            if (!$unsaved) {
                return null;
            } elseif (isset($value->id)) {
                return $value;
            } else {
                throw new \InvalidArgumentException(
                    "Cannot save property `$key` containing an API resource of type " .
                    get_class($value) . ". It doesn't appear to be persisted and is " .
                    "not marked as `saveWithParent`."
                );
            }
        } elseif (is_array($value)) {
            if (Util\Util::isList($value)) {
                // Sequential array, i.e. a list
                $update = [];
                foreach ($value as $v) {
                    array_push($update, $this->serializeParamsValue($v, null, true, $force));
                }
                // This prevents an array that's unchanged from being resent.
                if ($update !== $this->serializeParamsValue($original, null, true, $force, $key)) {
                    return $update;
                }
            } else {
                // Associative array, i.e. a map
                return Util\Util::convertToStripeObject($value, $this->_opts)->serializeParameters();
            }
        } elseif ($value instanceof StripeObject) {
            $update = $value->serializeParameters($force);
            if ($original && $unsaved && $key && static::getAdditiveParams()->includes($key)) {
                $update = array_merge(self::emptyValues($original), $update);
            }
            return $update;
        } else {
            return $value;
        }
    }

    public function jsonSerialize()
    {
        return $this->__toArray(true);
    }

    public function __toJSON()
    {
        return json_encode($this->__toArray(true), JSON_PRETTY_PRINT);
    }

    public function __toString()
    {
        $class = get_class($this);
        return $class . ' JSON: ' . $this->__toJSON();
    }

    public function __toArray($recursive = false)
    {
        if ($recursive) {
            return Util\Util::convertStripeObjectToArray($this->_values);
        } else {
            return $this->_values;
        }
    }

    /**
     * Sets all keys within the StripeObject as unsaved so that they will be
     * included with an update when `serializeParameters` is called. This
     * method is also recursive, so any StripeObjects contained as values or
     * which are values in a tenant array are also marked as dirty.
     */
    public function dirty()
    {
        $this->_unsavedValues = new Util\Set(array_keys($this->_values));
        foreach ($this->_values as $k => $v) {
            $this->dirtyValue($v);
        }
    }

    protected function dirtyValue($value)
    {
        if (is_array($value)) {
            foreach ($value as $v) {
                $this->dirtyValue($v);
            }
        } elseif ($value instanceof StripeObject) {
            $value->dirty();
        }
    }

    /**
     * Produces a deep copy of the given object including support for arrays
     * and StripeObjects.
     */
    protected static function deepCopy($obj)
    {
        if (is_array($obj)) {
            $copy = [];
            foreach ($obj as $k => $v) {
                $copy[$k] = self::deepCopy($v);
            }
            return $copy;
        } elseif ($obj instanceof StripeObject) {
            return $obj::constructFrom(
                self::deepCopy($obj->_values),
                clone $obj->_opts
            );
        } else {
            return $obj;
        }
    }

    /**
     * Returns a hash of empty values for all the values that are in the given
     * StripeObject.
     */
    public static function emptyValues($obj)
    {
        if (is_array($obj)) {
            $values = $obj;
        } elseif ($obj instanceof StripeObject) {
            $values = $obj->_values;
        } else {
            throw new \InvalidArgumentException(
                "empty_values got got unexpected object type: " . get_class($obj)
            );
        }
        $update = array_fill_keys(array_keys($values), "");
        return $update;
    }

    /**
     * @return object The last response from the Stripe API
     */
    public function getLastResponse()
    {
        return $this->_lastResponse;
    }

    /**
     * @param ApiResponse
     *
     * @return void Set the last response from the Stripe API
     */
    public function setLastResponse($resp)
    {
        $this->_lastResponse = $resp;
    }
}