Description:
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After update to PHP 5.6.10 with fix https://bugs.php.net/bug.php?id=68776 i can't set empty additional_headers for mail() function (i.e. if i want to set additional_parameters).

Test script:
---------------
echo 'without additional headers at all:';
var_dump(mail('to', 'subj', 'mess'));
echo 'with additional headers:';
var_dump(mail('to', 'subj', 'mess', 'X-Header: foo'));
echo 'with empty string as additional headers:';
var_dump(mail('to', 'subj', 'mess', ''));
echo 'with additional parameters and null as additional headers:';
var_dump(mail('to', 'subj', 'mess', null, 'foo'));



Expected result:
----------------
without additional headers at all:bool(true)
with additional headers:bool(true)
with empty string as additional headers:bool(true)
with additional parameters and null as additional headers:bool(true)

Actual result:
--------------
without additional headers at all:bool(true)
with additional headers:bool(true)
with empty string as additional headers:PHP Warning:  mail(): Multiple or malformed newlines found in additional_header in /tmp/test.php on line 9

Warning: mail(): Multiple or malformed newlines found in additional_header in /tmp/test.php on line 9
bool(false)
with additional parameters and null as additional headers:PHP Warning:  mail(): Multiple or malformed newlines found in additional_header in /tmp/test.php on line 11

Warning: mail(): Multiple or malformed newlines found in additional_header in /tmp/test.php on line 11
bool(false)