The "[]" were not the problem - the change was in how an array can be initialized (needing the explicit array() ).
Removing the braces would do harm. What the braces mean is "assign what's on the right side of the equal sign to the next element of the array". Here's an example of two pieces of code that do the same thing.
$example = array();
$example[] = "a";
$example[] = "b";
$example[] = "c";
$example = array();
$example[0] = "a";
$example[1] = "b";
$example[2] = "c";
In either case, you end up with three array elements, the indices are 0, 1, 2, and the values are "a", "b", "c".