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<?php $a1 = array("a" => array("1")); $a2 = array("a" => array()); var_dump(array_merge($a1, $a2)); var_dump(array_merge($a2, $a1));
based on oNqLS
Output for 4.3.0 - 7.2.0
array(1) { ["a"]=> array(0) { } } array(1) { ["a"]=> array(1) { [0]=> string(1) "1" } }