Thank you!

@tomadam @ondrejmirtes Even if the doc is saying that null is not a possible value, I can get some with

$commissionRateFile = new \SplFileObject($commissionRateFilePath);
$commissionRateFile->setFlags(\SplFileObject::SKIP_EMPTY | \SplFileObject::DROP_NEW_LINE);

You can see another example here: facebook/hhvm#5823

array(3) {
  [0] =>
  string(5) "row11"
  [1] =>
  string(0) ""
  [2] =>
  string(5) "row13"
}
array(3) {
  [0] =>
  string(5) "row21"
  [1] =>
  string(5) "row22"
  [2] =>
  string(5) "row23"
}
NULL

@VincentLanglet Your code example doesn't include fgetcsv call, I don't get how it's related to this method.

I meant

$commissionRateFile = new \SplFileObject($commissionRateFilePath);
$commissionRateFile->setFlags(\SplFileObject::SKIP_EMPTY | \SplFileObject::DROP_NEW_LINE);
while (!$commissionRateFile->eof()) {
    $line = $commissionRateFile->fgetcsv(';');
}

The last line of my csv was an empty line, and the last $line in my code was null.

Can it be null in all cases or only for some setFlags combination?

It's only related to some setFlags combination.

Without setFlags, I get [null].
With setFlags(\SplFileObject::SKIP_EMPTY | \SplFileObject::DROP_NEW_LINE), the empty lines was supposed to be skipped according to the doc, but it return null (instead of [null]).

You can look at the psalm code https://raw.githubusercontent.com/vimeo/psalm/master/dictionaries/CallMap.php

They are using list<string>|array{0: null}|false|null