Description:
------------
---
From manual page: http://www.php.net/intldateformatter.format
---

When an instance of \DateTimeImmutable is passed to \IntlDateFormatter's format() method, it doesn't format the date/time.

Please see the test script for a more accurate example, and check the last line of the "Actual result".

Test script:
---------------
<?php
$testDate = '2017-10-25 15:11:00';

$dateTime = \DateTime::createFromFormat('Y-m-d H:i:s', $testDate);
$dateTimeImm = \DateTimeImmutable::createFromFormat('Y-m-d H:i:s', $testDate);

$formatter = new \IntlDateFormatter('nl-NL', \IntlDateFormatter::FULL, \IntlDateFormatter::NONE);

var_dump($testDate);
var_dump($dateTime);
var_dump($formatter);
var_dump($formatter->format($dateTime));

var_dump($testDate);
var_dump($dateTimeImm);
var_dump($formatter);
var_dump($formatter->format($dateTimeImm));


Expected result:
----------------
string(19) "2017-10-25 15:11:00"
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-10-25 15:11:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(IntlDateFormatter)#3 (0) {
}
string(24) "woensdag 25 oktober 2017"
string(19) "2017-10-25 15:11:00"
object(DateTimeImmutable)#2 (3) {
  ["date"]=>
  string(26) "2017-10-25 15:11:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(IntlDateFormatter)#3 (0) {
}
string(24) "woensdag 25 oktober 2017"


Actual result:
--------------
string(19) "2017-10-25 15:11:00"
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-10-25 15:11:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(IntlDateFormatter)#3 (0) {
}
string(24) "woensdag 25 oktober 2017"
string(19) "2017-10-25 15:11:00"
object(DateTimeImmutable)#2 (3) {
  ["date"]=>
  string(26) "2017-10-25 15:11:00.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(16) "Europe/Amsterdam"
}
object(IntlDateFormatter)#3 (0) {
}
bool(false)