array_column null，但给出了2d数组

Question

Why is array_column warning me that it received a null in this snippet? It seems to get angry about what it receives inside of $hLA, but it's clearly a 2d array. The error I receive is: "PHP Warning: array_column() expects parameter 1 to be array, null given"

Values from a var_dump of $hLA:

$hL = pg_query("SELECT * FROM hubs");
$hLA = pg_fetch_all($hL);

function updateArticles($tP){
    global $hLA;
    $hmkey = array_search($tP['hm'], array_column($hLA, 'hm'));
}

array(4) {
  [0]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7F33B58C"
    ["hx"]=>string(1) "9"
    ["hy"]=>string(2) "14"
    ["zn"]=>string(6) "T1"
    ["r"]=>string(1) "n"
    ["a"]=>string(1) "n"
  }
  [1]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7FACBBFD"
    ["hx"]=>string(1) "1"
    ["hy"]=>string(1) "1"
    ["zn"]=>string(4) "R"
    ["r"]=>string(1) "y"
    ["a"]=>string(1) "n"
  }
  [2]=>
  array(6) {
    ["hm"]=>string(12) "5CCF7FADCE84"
    ["hx"]=>string(1) "8"
    ["hy"]=>string(1) "5"
    ["zn"]=>string(4) "Exit"
    ["r"]=>string(1) "n"
    ["a"]=>string(1) "y"
  }
}