Return Value Error - DatabaseAbstruct::buildQuery() return null but must be string

[casheeeewnuts]

This is:

- [x] a bug report

What is the expected behavior?

DatabaseAbstruct::buildQuery() return string

What is the current behavior?

DatabaseAbstruct::buildQuery() return null but it must be string, throwed Return Value Error

What are the steps to reproduce?

An error occurs when I try to export a spreadsheet with the following formula,

=AVERAGEIF(A:A, "", B:B)

when a blank cell is specified in the search condition.

<?php

require __DIR__ . '/vendor/autoload.php';

$reader = new \PhpOffice\PhpSpreadsheet\Reader\Xlsx();

// Create new Spreadsheet object
$spreadSheet = $reader->load('example.xlsx');

$writer = new \PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadSheet);
$writer->save('php://output'); // anywhere

// add code that show the issue here...

Which versions of PhpSpreadsheet and PHP are affected?

[PowerKiKi]

Fixed in 1.19.0