Fixed bug: in PHP versions less than 5.6.0, any request that didn't
attempt to add any groups would warn, because it would call array_fill()
with the second argument (num) equal to 0. From PHP 5.6.0, the num
argument to array_fill() is allowed to be 0.
Change-Id: I0c5772f15d8f550dc43fb37c3c58d15dd73ea584
