original_string: public function whereNull($column, bool $not = false, string $appendRule = 'AND'): self
      {
          $column = $this->checkStringValue('Argument $column', $column);
  
          $this->where[] = new NullCriterion($column, !$not, $appendRule);
          return $this;
      }
code: public function whereNull($column, bool $not = false, string $appendRule = 'AND'): self
      {
          $column = $this->checkStringValue('Argument $column', $column);
  
          $this->where[] = new NullCriterion($column, !$not, $appendRule);
          return $this;
      }
code_tokens: public function whereNull ( $ column , bool $ not = false , string $ appendRule = 'AND' ) : self { $ column = $ this -> checkStringValue ( 'Argument $column' , $ column ) ; $ this -> where [ ] = new NullCriterion ( $ column , ! $ not , $ appendRule ) ; return $ this ; }
docstring: Adds a IS NULL criterion to the WHERE section.
  
  @param string|\Closure|Query|StatementInterface $column Target column
  @param bool $not Whether the rule should be NOT NULL
  @param string $appendRule How the criterion should be appended to the others (SQL boolean operator name)
  @return $this
  @throws InvalidArgumentException
  @throws InvalidReturnValueException
docstring_tokens: Adds a IS NULL criterion to the WHERE section .