/** * Evaluates an expression and returns the value of the expression if the * expression evaluates to a non-null value. If the expression evaluates to * a null value, including instances of undefined values or missing fields, * returns the value of the replacement expression. * * The arguments can be any valid expression. * * @see http://docs.mongodb.org/manual/reference/operator/aggregation/ifNull/ * @see Expr::ifNull * @param mixed|Expr $expression * @param mixed|Expr $replacementExpression * @return self */ public function ifNull($expression, $replacementExpression) { $this->expr->ifNull($expression, $replacementExpression); return $this; }