Description:
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The script shows that json_encode function does not return FALSE on JSON_ERROR_UTF8 error as stated in manual page http://php.net/manual/en/function.json-encode.php but it returns "null" string.

Test script:
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$result = json_encode(iconv('UTF-8', 'UCS-2', "Příliš žluťoučký kůň úpěl ďábelské ódy."));
var_dump(json_last_error());
var_dump($result);

Expected result:
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int(5)
bool(false)


Actual result:
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int(5)
string(4) "null"