Description:
------------
There is an inconsistency between current PHP implemention and the documentation about Collator::__construct, Collator::create and collator_create.

It says:

Special values for locales can be passed in - if null is passed for the locale, the default locale collation rules will be used. If empty string ("") or "root" are passed, UCA rules will be used.

But actual implementation of collator_ctor in ext/intl/collator/collator_create.c does not check type of its parameter:

if( zend_parse_parameters( ZEND_NUM_ARGS() TSRMLS_CC, "s", &locale, &locale_len ) == FAILURE )
/* ... */
if(locale_len == 0) {
    locale = intl_locale_get_default(TSRMLS_C);
}

So, for PHP, a NULL value as an empty string imply the default locale.

Test script:
---------------
ini_set('intl.default_locale', fr_CA);

$coll = new Collator('');
var_dump(
    $coll->getLocale(Locale::VALID_LOCALE)
);

Expected result:
----------------
string(4) "root"

Actual result:
--------------
string(5) "fr_FR"