src/db/JoinClause.class.php
public function whereNull($column, $boolean = 'and', $not = false) {
		$null = $not ? 'not null' : 'null';
		
		return $this->on($column, 'is', $null, $boolean, false);
	}
public function whereNull($column, $boolean = 'and', $not = false) {
		$null = $not ? 'not null' : 'null';
		
		return $this->on($column, 'is', $null, $boolean, false);
	}
Add an "on where is null" clause to the join.

@param string $column
@param string $boolean
@return \queryBuilder\JoinClause