src/Syntax/Where.php
public function isNull($column)
    {
        $column = $this->prepareColumn($column);
        $this->isNull[] = ['subject' => $column];

        return $this;
    }
public function isNull($column)
    {
        $column = $this->prepareColumn($column);
        $this->isNull[] = ['subject' => $column];

        return $this;
    }
@param string $column

@return static