null, 'a' => 'second', 'd' => ['third'], 'fourth' => null, ], Arrays::normalize([ 1 => 'first', 'a' => 'second', 'd' => ['third'], 7 => 'fourth', ]), ); Assert::same( [ 'first' => true, '' => 'second', ], Arrays::normalize([ 1 => 'first', '' => 'second', ], filling: true), );